From Availability to Quality: Diagnosing Encounterability and Perceptual Affordance of the Built Environment in Xi’an’s Old City

Abstract

As urban development in China shifts toward improving existing areas, the focus of evaluation is moving from availability to quality, yet assessments of the neighborhood built environment and living circles still stop at facility provision. This study decomposes the conversion from spatial supply to need fulfillment into three links—availability, reach-and-visibility, and need fulfillment. Encounterability (E) captures how far a spatial element enters everyday experience through physical reach or visual exposure; perceptual affordance (P) captures how well an encountered element supports six perceptual needs: social interaction, recreation and leisure, aesthetic experience, emotional experience, broad learning, and humanistic enrichment. Taking Xi’an’s historic old city as a typical case, public needs were translated through grounded coding into auditable elements, which trained assessors evaluated at the city, district, and neighborhood levels, with a four-quadrant diagnosis locating the gaps. The results show that, within this context of comparatively rich provision, the principal experiential gaps arise at the encounter and support links: encounterability is similar across levels while perceptual affordance diverges, and the share of synergy categories differs significantly across levels (p = 0.007), forming resource–encounter, node–route, and frequency–support mismatches; the principal mismatch patterns are robust to equal weighting and to moderate shifts in the quadrant thresholds. Basic needs fail on quality and advanced needs fail on encounter and interpretation, pointing to three renewal actions: retrofitting, opening, and interpretation. This study extends evaluation objects from facilities to a fuller spectrum of spatial elements, extends encounter to reach and visibility together, and extends output from ranking to gap localization, offering a low-cost diagnostic tool for the human-centered assessment of the built environment, applicable to living-circle evaluation, urban physical examination, and livability improvement in historic neighborhoods.

1. Introduction

China’s urbanization has entered a stage of stock-based development, in which the focus of human-settlement construction is shifting from “whether it exists” to “how well it works”, and high-quality urban regeneration requires spatial supply to respond genuinely to people’s experiences, needs, and well-being [1]. Existing living-circle planning, however, concentrates on facility provision and seldom examines whether the built environment as provided actually supports people’s diverse needs. Between spatial supply and need fulfillment lie three successive links: whether a facility or space exists (availability); whether it can be conveniently reached or seen (reach-and-visibility); and whether, once reached, it satisfies people’s multiple needs (need fulfillment). Current evaluation systems remain largely at the first link; a small body of research has touched the second through perceived accessibility; and the third link—how space supports multiple perceptual needs—still lacks a systematic evaluation framework.

The key to the third link is understanding perceptual needs. The hierarchical nature of needs is a classic psychological proposition: Maslow ordered human needs from physiology and safety upward to belonging, esteem, and self-actualization [2]. Mapped onto urban space, environmental needs display a comparable hierarchy, from spaces that satisfy material and functional requirements, through spaces that carry emotion and atmosphere, to spaces that cultivate culture and spirit [3,4]; the emphasis also differs across population groups. Perceptual needs are nevertheless latent: they reside in psychological states and subjective experience, are difficult to observe directly, and are even harder to measure in the abstract, which is a major reason why the perceptual dimension has long been absent from spatial evaluation. A feasible path is translation—converting latent needs into observable spatial carriers and design elements, and then evaluating the encounter conditions and support capacity of these “high-perception” elements.

Xi’an’s historic old city is a typical setting for testing this path. First, the Ming city wall encloses a clearly bounded, well-structured study area (perimeter 13.74 km, area ca. 11.32 km²) that divides naturally into city, district, and neighborhood levels. Second, as the core of a capital for thirteen dynasties, historic remains, cultural landscapes, and dense everyday street life are superimposed here; perceptual elements are abundant, and spatial carriers can be found for every class of need. Third, its provision of facilities and public space ranks relatively high among Chinese old cities: the conditions of “availability” are close to the best, which makes “quality” worth investigating—resources are relatively rich, yet gaps in perceptual needs may persist—so the old city is an ideal sample for examining the three-link framework.

Accordingly, this study takes Xi’an’s old city as a case and tests, link by link, how spatial supply converts into need fulfillment. Three questions are addressed. First, how can diverse and latent perceptual needs be translated into auditable elements covering service facilities, the travel environment, and public space? Second, how can encounter conditions constituted jointly by reach and visibility be assessed on a common scale, distinguishing “reach-and-visibility” gaps from “need-fulfillment” gaps? Third, how can gaps at the city, district, and neighborhood levels be converted into differentiated renewal actions? Answering these questions supplies the missing link between “provision” and “experience” in stock-era evaluation of the built environment and provides a directly applicable diagnostic tool for people-centered old-city regeneration. The novelty of this study lies in combining three extensions within one audit framework: the objects of evaluation extend from facility inventories to a need-derived spectrum of facilities, travel environment, and public space; encounter is measured through reach and visibility on one audited scale, so that encounter gaps can be separated from support gaps; and the output turns from a composite ranking into a quadrant-based localization of the failing link. To our knowledge, no existing living-circle or built-environment assessment combines these three moves.

2. Literature Review

2.1. Availability: From Facility Provision to Multiple Spatial Objects

Since accessibility and spatial-equity research established the “facility–population” paradigm [5], facility counts, service radii, network distances, and population coverage have become standard indicators. The 15 min city elevated proximity into a comprehensive proposition of sustainability, livability, and health [6,7], and China’s living-circle planning translated it into an institutionalized practice of allocating facilities within walking rings [8,9]; recent studies have begun to incorporate street-view perception into living-circle walkability measurement [10], signaling an extension toward the experiential dimension. Overall, however, the objects of evaluation remain dominated by public service facilities—hospitals, schools, parks, elderly care, and retail—and the core question remains “whether it exists and how far it is”. From the perspective of perceptual experience, human perception does not occur only within facilities. The travel environment—living streets and the routes of school and work commutes—constitutes the most frequently contacted spaces of daily life; public spaces—squares, street corners, community gardens, and historic precincts—carry staying, interaction, and meaning. These are “high-perception” elements and key to fulfilling residents’ needs at different levels. In the current supply evaluation system, they neither enter facility inventories nor have corresponding provision indicators, even though they are critical to residents’ perceptual experience.

2.2. Reach-and-Visibility: From Calculated Accessibility to Perceived Encounter

Visibility and reachability are two distinct concepts. Perceived accessibility originated in transport research: in contrast to calculated accessibility based on network distance, it emphasizes an individual’s subjective judgment of “whether it can be obtained” [11]. Subsequent research clarified the mechanisms by which subjective judgment deviates from objective distance—individual capability, trip characteristics, and en-route environmental cues jointly shape perceived access [12]—and the perspective was later extended from public transport to walking environments, where safety, comfort, and interest significantly affect perceived walkability and the willingness to walk [13]. Visibility research, by contrast, focuses on view ranges and sight corridors: viewshed and eye-level greenness studies show that visible greenery at eye level and green area counted from above are two different exposures, and that visual contact itself produces restorative benefits [14]; street-view imagery and machine learning have made large-sample measurements of visual environmental quality feasible [15,16]. The two strands correspond to the two modes of encounter—reach and sight—but their objects differ: perceived-accessibility studies mostly take facilities and trip destinations as objects, whereas mountain silhouettes, skylines, and historic streetscapes enter daily experience mainly through being seen. Confronting a complex urban environment, reach and visibility therefore require different measurement arrangements for different elements. In this study, the term perceived accessibility is reserved for the residents’ self-reported judgments discussed above; the ratings collected in our audit are produced by trained assessors from environmental cues and are accordingly termed audited reachability and audited visibility (Section 3.3).

2.3. Need Fulfillment: From Environmental Quality to Need Support

Maslow’s hierarchy divides human needs into five ascending levels: physiological, safety, social, esteem, and self-actualization [2]. Within our discipline, scholars including Gibson [17], Bourdieu [18], and Rapoport [19] have probed the meaning of urban space, and their accounts converge on a layered reading. Gibson orders the meanings of the environment from primitive concrete and use meanings, through the meanings of instruments and the values or emotional meanings of settings, to the meanings carried by signs and symbols [17]. Bourdieu contrasts the physical attributes of phenomena with their symbolic meanings [18]. Rapoport divides the meaning of the built environment into low-level everyday and instrumental meanings; middle-level meanings of identity, status, wealth, and power; and high-level meanings anchored in cultural schemata and worldviews [19]. By depth of meaning, these accounts can be summarized as basic needs concerning matter and function, intermediate needs concerning emotion and atmosphere, and advanced needs concerning spirit and culture. Later scholars have produced substantial research on spatial qualities such as safety, inclusiveness, vitality, beauty, place attachment, restoration, and historic culture [20,21,22,23,24], yet most of it addresses a single quality or a single type of place, whereas human needs and everyday life spaces are diverse and systemic and call for a systemic response. Drawing on Wang’s studies [25,26], this study organizes needs in urban space along a continuous spectrum: basic needs of social interaction and recreation-and-leisure that accompany daily activity; intermediate needs of aesthetic experience and emotional experience at the level of body and mind; and advanced needs of broad learning and humanistic enrichment—and on this basis, constructs the urban spatial elements that support them. This spectrum is a spatially oriented reinterpretation of needs theory rather than a direct operationalization of Maslow’s hierarchy: the tiers are ordered by the depth of meaning that everyday space must sustain—the layered structure documented above—rather than by motivational priority. Social interaction and recreation-and-leisure are basic in this spatial sense because they arise in the course of routine daily activity and can be supported by generic physical settings; aesthetic experience and emotional experience are intermediate because they depend on environmental qualities that must be perceived and felt beyond functional use; broad learning and humanistic enrichment are advanced because space supports them only through symbolic and cultural mediation such as interpretation and programming. The six needs and their tiering follow the classification developed and tested in prior studies of urban perceptual experience [25,26].

In summary, this study proposes a three-link analytical framework of “perceptual elements–encounterability–perceptual affordance” (Figure 1). It takes service facilities, the travel environment, and public space as the complete spectrum of perceptual elements; operationalizes “reach-and-visibility” as encounterability (E), the degree to which a perceptual element enters daily experience through reach or sight; and operationalizes “need fulfillment” as perceptual affordance (P), the degree to which an encountered space supports the six perceptual needs. Evaluation proceeds at the city, district, and neighborhood levels and leads to correspondingly differentiated renewal actions. Availability—whether elements exist at all—is documented through the element inventory and treated as a contextual precondition rather than as a third scored axis: the old city is examined precisely because its provision is comparatively rich (Section 1), so the framework interrogates how existing supply converts into experience rather than whether supply is sufficient.

3. Research Design and Methods

3.1. Study Area and Assessment Levels

The study area is the old city of Xi’an enclosed by the Ming city wall (perimeter 13.74 km, area ca. 11.32 km²), where housing, commerce, tourism, and public services are densely superimposed. According to residents’ daily activity ranges, three nested assessment levels were defined (Figure 2): the city level covers the entire walled area, roughly corresponding to walking activity of 30 min or more, and concerns the overall structure and scarce resources; the district level takes the Wulukou area, roughly a 15 min activity unit, and concerns facility nodes and daily routes; and the neighborhood level takes the Qixianzhuang community, roughly a 5 min high-frequency unit, and concerns near-home streets and corners. The three levels share the six need classes and a common scale, while the audited objects vary by level. The district- and neighborhood-level units were selected by three criteria: functional completeness—each contains the full range of element classes required by the audit, covering service facilities, travel environment, and public space; everyday character—both are predominantly residential in daily use rather than tourism showcases, so that scores reflect ordinary rather than visitor-oriented conditions; and structural typicality—their density, street pattern, and facility mix are characteristic of the residential quarters of the old city. The Wulukou area, at the north-eastern corner of the walled city, approximates a 15 min walking range centered on its metro station and combines parks, a sports stadium, commercial complexes, and a revolutionary-memorial precinct with ordinary residential blocks; the Qixianzhuang community approximates a 5 min walking range adjoining Revolution Park and consists of several aged residential compounds typical of the old city’s neighborhoods. They are read as typical units of their levels rather than statistically representative samples; the implications of auditing one unit per level are discussed in Section 6.

3.2. Translating Needs into Elements

The translation rests on affordance theory: the value of an environment lies in the action possibilities it offers its users [27], so latent needs can be observed and evaluated through the spatial objects that carry them. Translation follows the principle of fixed needs, local carriers: the six perceptual needs serve as stable analytical dimensions, while their spatial carriers vary with city and level and must be identified locally.

Translation proceeded in three steps. Step 1, need identification: questionnaires and semi-structured interviews were administered face to face in subdistrict sampling zones covering the walled city, with quotas stratified in proportion to the approximate age structure of the old city’s resident population (children:adolescents:adults:older adults ≈ 2:2:3:3), with stratification also covering gender, occupation, and income. After 20 pilot sessions (25–30 June 2021), the formal survey ran intermittently from July 2021 to October 2022; each session lasted 5–30 min, children under seven were interviewed through their caregivers, and collection continued until additional documents no longer changed the category statistics appreciably. Of 420 documents collected, 407 were valid (96.9%); each document combines one respondent’s questionnaire and short semi-structured interview, covering children (19.7%), adolescents (21.8%), adults (27.8%), and older adults (30.7%), with a balanced gender composition (48.2% male) and a majority of long-term residents (41.5% residing over ten years). The documents were coded item by item following grounded-theory procedures by three coders, using the six needs as top-level categories: each need expression was assigned to a need dimension and tagged with the spatial object it pointed to and its mention frequency, and coding disagreements were resolved by discussion until consensus. The questionnaire and the interview outline are provided in Supplementary Text S1. Step 2, carrier induction: the 48 secondary space types obtained from open coding were consolidated through axial coding into carriers—the semantic bridges between needs and space—by merging space types that share a dominant need and a similar activity setting, with consolidation continuing until no new carrier emerged; the full coding framework with mention frequencies is given in Supplementary Table S1. Step 3, level mapping: carriers were mapped onto auditable elements according to the activity range of each level—a category was retained at a level only when its carrier both falls within that level’s activity range and is observable on site; elements are organized with imagery vocabulary at the city level—landmarks, paths and edges, and districts and nodes [28]—and with functional vocabulary at the district and neighborhood levels—public service facilities, travel environment, and public space. The translation finally produced 18 carriers, 48 secondary space types, and 32 auditable element categories (11 at the city level, 10 at the district level, and 11 at the neighborhood level); the results are reported in Section 4.1.

3.3. Measuring Encounterability and Perceptual Affordance

The supply side was assessed through on-site spatial audit [29,30], whose objects are observable properties of the environment rather than users’ subjective feelings. The audit indicators were constructed in two steps. First, the observation content of each dimension was derived from the definitions of the six needs, and its relative importance within each dimension was weighted by an analytic hierarchy process: six experts holding doctoral degrees in urban design completed pairwise comparison matrices, the weights were taken as the principal eigenvectors of the judgment matrices, and all matrices passed the consistency test (consistency ratio ≤ 0.10). Second, the weighted content was integrated into scoring anchors on a 1–5 scale (

Table 1. Audit dimensions, observation content, and scoring anchors.

Dimension (Entropy Weight)	Observation Content (Construction Weight)	Scoring Anchors (1–5) 1
Social interaction (0.1634)	Number of seats (0.54); seating comfort (0.30); staying-support facilities (0.16)	No seating (1); 1–4 basic seats (3); ≥5 comfortable seats supporting conversation (5)
Recreation and leisure (0.2697)	Number of play facilities (0.67); playfulness of design (0.33)	None (1); 1–2 types, limited interest (3); ≥3 types, engaging, all ages (5)
Aesthetic experience (0.1434)	View corridors (0.54); art installations (0.30); art venues (0.16)	Blocked corridors, no art (1) partly open, 1–2 pieces (3) open corridors, ≥3 elements (5)
Emotional experience (0.1272)	Inclusive care design (0.67); psychological comfort spaces (0.33)	No care design (1); 1–2 barrier-free items (3); ≥3 items plus restorative features (5)
Broad learning (0.1927)	Learning facilities (0.54); activity frequency (0.30); business diversity (0.16)	No facilities or activities (1); facilities present, few activities (3); open, diverse, frequent (5)
Humanistic enrichment (0.1036)	Richness of historic remains (0.54); legibility of the landscape structure (0.30); continuity of commemorative places (0.16)	No historic-cultural elements (1); scattered, 1–2 interpretive signs (3); legible structure, concentrated heritage, ≥3 signs (5)
Encounterability E: audited reachability	Ease of reaching (en-route safety, comfort, and interest as cues)	Long detours, very hard to reach (1); some effort needed (3); nearby or en route, easy to reach (5)
Encounterability E: audited visibility	Frequency of appearing in the daily field of view	Almost never visible (1); occasionally visible (3); frequently visible (5)

¹ Anchors are defined at scores 1, 3, and 5 for every dimension; a score of 2 or 4 is assigned when the observed condition falls between the adjacent anchors. The same rule applies to the two encounterability items.

); the complete audit form and scoring rules are provided in Supplementary Table S2. Residents’ need expressions form the basis of translation (Section 3.2), while the supply conditions of space were rated independently by three uniformly trained assessors from the research group—one a native resident of the old city and two with prior project experience in it. Training followed a systematic observation protocol with standardized procedures, operational definitions for every observed item, and uniform recording standards, and assessors qualified when pre-audit trial ratings agreed with the training standard on at least 95% of items. The audit completed 323 observations (201 at the city level, 83 at the district level, and 39 at the neighborhood level) with 646 photographs archived. Inter-rater reliability was computed for every audit item—kappa coefficients for categorical judgments and intraclass correlation coefficients for ordinal ratings, the latter selected and reported following Koo and Li [31]—and 83.2% of items reached the acceptance threshold of κ or ICC ≥ 0.40, corresponding to at least moderate agreement on the benchmarks of Landis and Koch [32]. The audit implementation and reliability protocol is documented in Supplementary Text S2.

Measurement covers two axes. Encounterability (E) combines audited reachability and audited visibility. Both are rated by the trained assessors from environmental cues rather than reported by residents; the qualifier audited keeps these expert-audit measures distinct from perceived accessibility, which in the literature denotes users’ own judgments [11,12]. Audited reachability rates the ease of reaching, with en-route safety, comfort, and interest as reference cues; audited visibility rates the frequency with which an element appears in the everyday field of view. Parks and streets enter daily experience mainly by reach, and mountains and skylines mainly by sight; uniform anchors keep the ratings comparable across elements. Perceptual affordance (P) is scored separately for the six needs, with the observation content listed in Table 1; a dimension is marked not applicable—rather than scored low—when its valid observations fall below 10% of an element’s records; this floor prevents a dimension score from resting on one or two incidental observations, which would both penalize elements for needs they are not expected to serve and make scores unstable. In total, 102 valid dimension scores were retained. Dimensions are aggregated with entropy weights (Equations (1) and (2)) [33]: indicator construction is entrusted to professional judgment, and weighting to variation in the data, avoiding subjective disputes over the importance of dimensions.

$$e_d=-(1/ln{n}_d)\Sigma p_{jd}\mathrm{l}\mathrm{n}{p}_{jd}$$

(1)

$$w_d=(1-e_d)/\Sigma (1-e_d)$$

(2)

where $p_{jd}$ is the score share of element j on dimension d, $n_d$ the number of valid elements on dimension d, $e_d$ the information entropy, and $w_d$ the entropy weight.

3.4. Dual-Axis Diagnosis and Optimization

Observation scores are summarized into category scores and converted into a common 1–5 reporting scale (Equation (3)); composite perceptual affordance is the entropy-weighted mean over applicable dimensions (Equation (4)).

$$L_{j}d=1+0.8·I_{j}d;E_j=1+0.8·I_j^E$$

(3)

$$P_j=\Sigma (d\in D_j)w_d·L_{j}d/\Sigma (d\in D_j)w_d$$

(4)

where $I_{j}d$ is the summarized index of element j on dimension d, $I_j^E$ the summarized encounterability index, and $D_j$ the set of applicable dimensions of element j.

Crossing E and P at the fixed midpoint of 3.0 yields four diagnoses (Figure 3). The midpoint is criterion-referenced: both axes are reported on the same 1–5 anchored scale, on which 3 denotes the anchored neutral condition (reachable with some effort; partial, limited support), so 3.0 marks the boundary between supportive and unsupportive states; a data-driven cut such as the sample mean or median would let quadrant membership drift with the composition of audited elements and would prevent comparison across levels and audit rounds. The synergy type (high E, high P) calls for maintenance and fine-tuning; the quality-constrained type (high E, low P) prioritizes improving staying conditions and activity programming; the encounter-constrained type (low E, high P) prioritizes entrances, view corridors, and connections; and the dual-constrained type (low E, low P) requires integrated renewal. The matrix shares its classificatory form with importance–performance analysis [34], but both axes here are environmental audit measures, and the purpose of the crossing is to locate the failing link rather than to rank improvement priorities. Compositions of quadrant types are compared across levels with a permutation test: level labels are randomly reallocated across the 32 categories, the χ² statistic of the level-by-quadrant table is recomputed for each of N = 100,000 permutations, and the p-value is the share of permuted statistics at least as large as the observed one—a procedure that remains valid for the small cell counts here, for which asymptotic χ² approximations are unreliable; for the synergy-share comparison, the permutation null distribution was additionally enumerated exactly. The sensitivity of the diagnosis to the weighting scheme and to the threshold value is examined in Section 4.4. Diagnostic results are reported in Section 4 and the corresponding optimization strategies in Section 5.

4. Results

4.1. High-Perception Spatial Elements of Xi’an’s Old City

The translation yields the spectrum of perceptual needs and spatial elements for Xi’an’s old city (Figure 4). On the need side, all four age groups express all six needs, but with different emphases: children and older adults concentrate on the basic needs of social interaction and recreation, tightly bound to near-home spaces; adolescents and adults express more intermediate and advanced needs and point to a wider spatial range. On the element side, the mentioned frequencies reveal where perceptual needs concentrate: educational venues (87.3%), public centers (81.0%), landscape nodes (67.3%), commemorative spaces (66.3%), and living streets (64.3%) form the most frequently cited group of carriers and can be regarded as the high-perception spatial elements of the old city.

The spectrum shows two localized features of Xi’an’s old city. First, basic needs rely heavily on informal spaces: social interaction points to public centers and living streets far more often than to formal service facilities (13.1%); community entrances and street corners carry abundant spontaneous interaction, and residents bringing their own chairs to gather is a common observation—an inventory-based evaluation would miss these carriers entirely. Second, carriers of advanced needs are unusually rich: commemorative spaces and historic remains (43.7%) rank high in the humanistic-enrichment dimension, and several interviewees described gazing from the city wall toward the Bell Tower and the Qinling Mountains as a core image triggering local identity—a spectrum signature of resource-dense historic cities.

After level mapping, the composition and distribution of the 32 audited element categories are shown in Figure 5: 11 categories at the city level, organized as landmarks, paths and edges, and districts and nodes; 10 at the district level; and 11 at the neighborhood level, organized as public service facilities, travel environment, and public space. The element list derives from residents’ actual expressions rather than a priori assumptions, delimiting an audit scope consistent with everyday experience.

4.2. Encounterability and Perceptual Affordance Across the Three Levels

Table 2. Six-dimension scores, encounterability (E), perceptual affordance (P), and quadrant diagnoses of the 32 audited element categories.

Unit	No.	Element Category	SI	RL	AA	EE	BL	HE	E	P	Quadrant
City	1	Landscape landmarks	—	—	4.65	—	—	2.77	1.74	3.86	B-II
	2	Landmark buildings	—	—	3.25	2.33	2.50	2.10	4.24	2.58	B-I
	3	Cultural landscapes	—	3.66	2.78	3.14	2.69	2.38	3.84	3.05	A
	4	Recreational greenways	—	4.21	3.90	3.58	—	—	2.58	3.98	B-II
	5	Axial structure	—	—	2.16	—	—	1.65	3.15	1.95	B-I
	6	Distinctive streets	—	3.17	2.62	2.69	1.98	2.18	2.46	2.61	C
	7	Scenic views	—	—	4.06	3.84	—	2.70	2.77	3.61	B-II
	8	Gateway spaces	—	2.13	3.18	3.03	—	—	3.37	2.62	B-I
	9	Parks/squares	—	4.50	4.24	3.41	2.86	2.54	2.26	3.67	B-II
	10	Key urban nodes	—	—	1.92	—	—	—	3.06	1.92	B-I
	11	Cultural and arts facilities	—	—	4.22	—	4.13	3.10	1.89	3.92	B-II
District	1	Commercial and leisure facilities	3.23	4.16	2.62	—	3.06	—	3.73	3.40	A
	2	Educational and cultural facilities	—	—	3.50	—	4.15	3.01	2.89	3.67	B-II
	3	Sports facilities	3.15	4.27	—	—	2.61	—	3.15	3.47	A
	4	Healthcare and social welfare	—	—	—	4.38	—	—	3.07	4.38	A
	5	Children’s school routes	3.26	2.24	—	—	1.87	—	2.45	2.39	C
	6	Adult commuting routes	—	—	2.37	2.16	—	—	3.56	2.27	B-I
	7	Older adults’ daily-life routes	2.54	2.00	2.98	—	—	—	3.25	2.40	B-I
	8	Historic and cultural precincts	2.69	2.78	3.74	4.14	3.62	3.26	2.85	3.29	B-II
	9	Parks/squares	4.05	4.53	4.70	3.63	3.10	3.18	3.30	3.94	A
	10	Entrances to public facilities	—	—	3.38	2.90	—	—	3.50	3.15	A
Neighborhood	1	Everyday service facilities	2.69	—	—	3.10	—	—	3.66	2.87	B-I
	2	Educational and cultural facilities	—	—	2.57	—	4.54	—	2.77	3.70	B-II
	3	Community service complexes	1.82	1.74	—	—	—	—	2.13	1.77	C
	4	Mixed commercial and business facilities	2.50	2.86	—	—	1.89	—	2.65	2.46	C
	5	Residential streets	2.26	2.08	—	1.82	—	—	4.22	2.07	B-I
	6	School streets	2.38	2.00	2.24	—	—	—	3.25	2.17	B-I
	7	Recreational greenways	2.54	3.07	4.06	3.25	—	3.01	2.33	3.16	B-II
	8	Back lanes	1.68	1.50	—	—	—	—	3.10	1.57	B-I
	9	Street-front open spaces/corners	2.53	2.34	—	—	—	—	3.50	2.41	B-I
	10	Neighborhood parks	4.70	4.78	4.50	3.38	3.17	3.62	2.88	4.12	B-II
	11	Community/school entrances	2.61	2.32	—	2.06	—	—	4.54	2.34	B-I

Note: SI = social interaction; RL = recreation and leisure; AA = aesthetic experience; EE = emotional experience; BL = broad learning; HE = humanistic enrichment; “—” = not applicable. A = synergy; B-I = quality-constrained; B-II = encounter-constrained; C = dual-constrained.

reports the 102 valid scores and quadrant diagnoses of the 32 element categories. Mean E is similar across levels—2.85 (city), 3.17 (district), 3.18 (neighborhood)—whereas mean P diverges markedly at 3.07, 3.24, and 2.60. Quadrant compositions differ still more: the city level counts one synergy, four quality-constrained, five encounter-constrained, and one dual-constrained category; the district level is led by five synergy categories; and the neighborhood level has no synergy category and six quality-constrained ones. The city and the neighborhood have similar problem counts but opposite directions: the city is marked by “valuable but rarely encountered” and the neighborhood by “frequently encountered but weakly supporting”. Because the audited object sets differ by level—imagery elements at the city level, and facility, route, and public-space elements below—cross-level differences in mean E and P combine scale effects with composition effects; they are read here as contrasts between level-specific element portfolios rather than as pure effects of spatial scale.

City level: the resource–encounter mismatch (Figure 6). Of 11 categories, only cultural landscapes reach the synergy type (E 3.84, P 3.05), and the advantage is modest. The encounter-constrained type concentrates the most valuable resources: landscape landmarks score P 3.86—with 4.65 on the aesthetic dimension, the highest in the table—but E only 1.74, as the view of the Qinling Mountains from the wall has nearly left daily sight owing to occlusion and reduced visibility; cultural and arts facilities score P 3.92 against E 1.89, their concentrated distribution leaving most precincts in a service blind zone; and parks and squares (2.26/3.67), recreational greenways (2.58/3.98), and scenic views (2.77/3.61) belong to the same group. The quality-constrained type points the other way: landmark buildings reach E 4.24 but P 2.58—architectural value has not converted into support for emotion, learning, or enrichment; the axial structure (3.15/1.95) is heavily commercialized with cultural functions absent; and key urban nodes are traffic-dominated and barely allow staying. Distinctive streets are low on both axes, the dual-constrained type. For the audited categories, the binding city-level constraint is thus not whether resources exist but whether they enter daily experience and can be understood once encountered.

District level: the node–route mismatch (Figure 7). Public service facilities and public spaces perform well: parks and squares (3.30/3.94) are the only category valid and balanced on all six dimensions; healthcare and welfare reaches 4.38 on emotional experience; commercial and leisure (3.73/3.40), sports facilities (3.15/3.47), and facility entrances (3.50/3.15) all reach synergy. Educational and cultural facilities (2.89/3.67) and historic precincts (2.85/3.29) are encounter-constrained; the latter’s emotional-experience score of 4.14 shows that commemorative places support well once reached—the problem is reaching them. The travel environment contrasts sharply: children’s school routes (2.45/2.39) are dual-constrained; adult commuting routes (3.56/2.27) and older adults’ daily routes (3.25/2.40) are quality-constrained. All three routes formed spontaneously—schooling attaches to schools, commuting to the metro, and elderly life to hospitals and supermarkets—and the district level has never treated routes as design objects. High-scoring nodes do not automatically extend into high-quality movement.

Neighborhood level: the frequency–support mismatch (Figure 8). The six quality-constrained categories are all daily must-pass spaces: residential streets score E 4.22 but P only 2.07; community and school entrances reach E 4.54, the highest in the table, with P at 2.34; back lanes have the table’s lowest P at 1.57; and school streets, street corners, and daily service facilities join the list. The six high-frequency categories average E 3.71 but P only 2.24—the most frequently encountered spaces are precisely the weakest in support. Social interaction and recreation generally fall below 2.6, consistent with field records of residents bringing chairs and gathering spontaneously at corners: the need exists, but the conditions are absent. The encounter-constrained type concentrates almost all the neighborhood’s high P scores: neighborhood parks reach P 4.12—with interaction 4.70 and recreation 4.78 inside the park—but E only 2.88, as residents to the north, nearest in straight-line distance, must detour to enter; educational and cultural facilities score 4.54 on broad learning against E 2.77, learning resources sitting outside daily movement lines. Community service complexes (2.13/1.77) and mixed commercial facilities are dual-constrained. The neighborhood picture: quality collapses in the most everyday places, while valuable resources sit beyond a detour.

4.3. Gap Types and Structural Analysis

Quadrant composition differs across levels (

Table 3. Diagnostic structure and principal mismatch of the three levels.

Level	Quadrants (A/B-I/B-II/C)	Mean E/P	Principal Mismatch	Action Orientation
City	1/4/5/1	2.85/3.07	Resource–encounter	Protect view corridors; open entrances; connect slow routes; layered interpretation
District	5/2/2/1	3.17/3.24	Node–route	Stitch facility nodes together along the three daily routes
Neighborhood	0/6/3/2	3.18/2.60	Frequency–support	Add seating, shade, and play to streets, corners, and entrances

). The city level is dominated by the encounter-constrained type (5/11), the neighborhood level by the quality-constrained type (6/11), and synergy takes half at the district level (5/10). Permutation tests show a significant cross-level difference in the share of synergy categories (χ² = 9.62, p = 0.007), whereas the difference in the full four-quadrant composition does not reach significance at the 0.05 level (χ² = 11.10, p = 0.082) and is treated as suggestive only; the cross-level statements below therefore rest on the synergy-share contrast and on the descriptive patterns of Table 3. The same need fails differently at different levels: recreation fails on encounter at the city level, where parks and greenways are encounter-constrained, and on quality at the neighborhood level, where streets and corners are quality-constrained. The three mismatches form a continuous transmission chain—the city organizes resources, the district builds connections, the neighborhood carries high-frequency activity—and a break in any link leaves availability as mere potential.

Encounter constraints have two sources. The sight type: resources exist but have left the daily field of view—landscape landmarks are occluded by buildings and limited by visibility, and the wall-top view has not become an everyday facility because of ticketing. The reach type: resources are visible but hard to enter—parks are unevenly distributed and demand long detours, greenways rely on the moat park and serve the inner city poorly, cultural and arts facilities cluster in the Sanxue Street corner, and neighborhood parks are near yet hard to reach. Historic precincts combine both: peripheral in location and static in display; they lack permeable interfaces toward the district. The two sources appear to differ in policy nature: sight-type constraints are mainly associated with management and institutional arrangements—ticketing, opening hours, and height control—whereas reach-type constraints are mainly associated with spatial structure—entrances, connections, and distribution; the audit records these associations but cannot by itself establish the underlying causes. Opening one viewing point costs far less than building a park, yet it can activate stock resources whose P approaches 4.0.

Quality constraints follow a level gradient. Their share is 36% (city), 20% (district), and 55% (neighborhood), and their nature changes: at the city level, the deficit is interpretation—landmark buildings and axes are visible and reachable, but humanistic enrichment averages only 2.43 and visual recognition fails to become understanding; at the district level, the deficit is routes, concentrated on the three daily lines; and at the neighborhood level, the deficit is staying—seats, shade, and playable facilities. Repair costs fall and benefit frequencies rise down this gradient. The gradient also carries a distributional meaning: children and older adults, with the smallest activity ranges and the deepest reliance on near-home space, together make up 50.4% of the sample and live precisely at the level where quality constraints concentrate; the more frequently a space is encountered, the less design investment it tends to receive.

Gap types correspond to need tiers. Basic needs fail on quality: the deficits of social interaction and recreation concentrate in neighborhood-level quality constraints, where carriers are abundantly present but staying conditions are absent. Advanced needs fail on encounter and interpretation: the deficits of broad learning and humanistic enrichment concentrate at the city level, where resources are hard to encounter or lack interpretation and participation once encountered. Intermediate needs sit between: the high-scoring carriers of aesthetic and emotional experience are mostly encounter-constrained—beautiful but rarely met. Quadrants decide whether to fix connection or quality first; dimension scores decide what exactly to supplement. Basic needs call for retrofitting, intermediate needs for opening, and advanced needs for interpretation—this correspondence opens the discussion in Section 5.

4.4. Robustness of the Diagnosis to Weighting and Threshold Choices

Two checks examine whether the diagnosis depends on the analytical choices of Section 3, using the category scores of Table 2. The first replaces the entropy weights with equal weights over each element’s applicable dimensions. Equal-weight affordance scores are nearly identical to the entropy-weighted ones (Pearson r = 0.996; mean absolute difference 0.07, maximum 0.16 on the 1–5 scale), and only 1 of the 32 categories changes quadrant: cultural landscapes, the single city-level synergy category, whose affordance falls from 3.05 to 2.93 and whose diagnosis shifts to quality-constrained—consistent with Section 4.2, which already notes that its synergy advantage is modest. The three principal mismatches are unchanged, and the cross-level difference in synergy share remains significant (p < 0.01).

The second check shifts both quadrant thresholds by ±0.2, i.e., by 5% of the scale range. At 2.8, four categories move, all into the synergy type—two at the district level, strengthening its synergy lead to 7 of 10 categories, and two at the neighborhood level—while the city-level composition is unchanged, the quality-constrained type remains the largest neighborhood group, and the synergy-share difference remains significant (p < 0.01). At 3.2, eight categories move and the synergy type nearly empties at all levels (0, 2, and 0 categories), so the synergy-share contrast weakens to marginal (p ≈ 0.09); the city level nevertheless remains dominated by encounter-constrained categories (5 of 11) and the neighborhood level by quality-constrained categories (5 of 11) with no synergy category. Overall, 12 of the 32 categories lie within 0.2 of a threshold on at least one axis, but the two signatures on which the interpretation rests—encounter-constrained categories concentrating at the city level and quality-constrained categories concentrating at the neighborhood level, with synergy absent there—hold under every variant; the size of the district-level synergy lead is the component most sensitive to a stricter cut, and the discussion in Section 5 does not depend on its exact magnitude.

5. Discussion

5.1. Organizing Urban Space by Perceptual Needs

The first implication of the spectrum is a reconstruction of evaluation objects. Evidence from Xi’an’s old city shows that the spaces carrying perceptual needs extend far beyond public service facilities: the high-frequency carriers of social interaction are public centers and living streets, many of them informal spaces—entrances and corners—that appear on no facility inventory; the carriers of aesthetics and humanistic enrichment are mountains, axes, and historic remains, objects that provision indicators cannot describe. Organizing evaluation by facility category congenitally misses most places where perception occurs; organizing it by needs makes the object set complete. The theoretical basis is explicit: affordance theory holds that the value of an environment lies in the actions it opens to people [27], and the needs hierarchy suggests that human claims progress from material access to meaning [2]; an evaluation that stops at the facility layer acknowledges only the bottom of the pyramid. The long-standing claim of public-space research thus lands operationally: people’s needs define the value of space, rather than facility inventories defining people’s needs [35,36].

The second implication is a supplement to planning instruments. Coding frequencies locate where attention concentrates, and educational venues, public centers, landscape nodes, and commemorative spaces constitute the old city’s high-perception elements. This list can be read as the needs edition of urban-image research: Lynch depicted the visual skeleton of the city through imageability, answering what is remembered [28]; the high-perception list depicts the experiential skeleton through need-bearing, answering what is needed. The two are complementary—one serves formal cognition, the other renewal decisions. For perception-measurement research, the list supplies a missing sampling frame: street views and machine learning can measure environmental quality at scale [15,16], but what and where to measure has long depended on researchers’ assumptions; an element list generated from public documents aims to measure where needs actually land, turning coverage into diagnosis. For living-circle practice, it complements the facility checklist—one manages experience, the other function—filling the blind zone of defining supply based on facility items [8,9,10].

It should be stressed that the spectrum is a local product. The six needs and the three-tier structure travel across cases, but carrier composition and frequencies necessarily vary: Xi’an’s advanced-need carriers are unusually rich because of its capital heritage, and the spectrum of an ordinary city may center elsewhere. Applying the framework elsewhere requires rebuilding the local spectrum from comparable public documents rather than transplanting Xi’an’s element list.

5.2. How the Three Mismatches Form

The three mismatches correspond to different break points on the path from resource to experience. The city-level resource–encounter mismatch breaks between provision and encounter: mountains and vistas are constrained by occlusion, visibility, and ticket thresholds; parks and cultural facilities by uneven distribution and detour distance. This finding enters the current debate on proximity planning: advocates reorganize urban services around proximity [6,7], while critics use mobility data to question the equation of proximity with use [37]. The Xi’an evidence suggests a middle position: proximity is a valid goal, but its delivery depends on deliberate design of encounter conditions—perceived access deviates systematically from calculated distance [11,12], visual contact is an exposure channel independent of reach [14], and compact form shortens only nominal distance, powerless against occlusion, ticketing, entrances, and interpretation. The interpretation deficit of historic resources is the cultural version of the same break: the historic urban landscape approach has long urged that heritage management face daily life [38]; residents and tourists attend to different cues [39]; and without the mediation of interpretation, activity, and participation, conserved heritage remains upstream in the value-realization chain [40].

The district-level node–route mismatch breaks between facilities and movement. Nodes perform well while all three routes fall into problem quadrants. A plausible institutional reading—one the audit itself cannot verify—is that construction and management are bounded by facility parcels: someone is responsible inside each parcel, while no actor claims the cross-parcel linear spaces. Yet, residents’ daily experience is composed of complete travel chains, where safety, comfort, and interest shape every walk [13]. Place-value research offers a matching judgment: quality is the product of sustained cross-parcel governance, not of single-point construction [41]; the low scores of the three routes give that judgment level-specific proof and argue for treating routes as renewal objects of equal rank with facilities.

The neighborhood-level frequency–support mismatch breaks between encounter and staying. Residential streets and entrances are passed daily yet lack seats, shade, and playability; residents bringing their own chairs is spontaneous compensation for absent staying conditions. Public-space research long ago established that staying depends on details rather than area [21,42]. More noteworthy is the distributional meaning. Environmental-justice research mostly addresses inequities of quantity and distance [43]; the evidence here reveals a third dimension: frequency. Children and older adults, most dependent on the neighborhood level, are served least, while renewal investment has long flowed to landmarks and gateways serving the groups with the most alternatives; weighted by use frequency, the quality inequality of the old city is more severe than facility coverage suggests. The inversion between design attention and use intensity should become a corrective criterion in ordering renewal resources.

The three break points admit a common institutional interpretation: governance is organized by parcels and inventories, and experience by chains and frequencies, and the observed mismatches are consistent with a misalignment of these two logics; verifying this mechanism would require governance and management data beyond the audit.

5.3. Optimization Strategies

The strategies in this subsection are design propositions inferred from the audit diagnosis, not interventions whose effects this study has tested; propositions that involve governance or institutional change are noted as such, since their feasibility lies beyond the audit evidence. Diagnosis types directly order the actions. Quality-constrained elements come first with micro-retrofitting—low cost, high benefit frequency; one entrance retrofit serves hundreds of passages a day. Encounter-constrained elements come next with opening and connecting—almost no construction is needed to activate stock resources whose P approaches 4.0. Dual-constrained elements enter integrated renewal, treating provision, connection, and quality together; synergy elements are maintained to prevent regression through changed opening hours or management rules. This order reverses the customary practice of starting from landmarks and gateways, yet it is closer to everyday well-being.

At the three levels, the strategies have distinct handles (Table 3). The city level centers on encounter conditions: bring the Qinling–city-wall view corridors into height control and skyline guidance, open the wall-top vista in time slots, supplement cultural and arts facilities toward service blind zones, and extend the moat greenway into the inner city; build interpretation in layers—signage for those who arrive, programmed activities for participants, and digital guides for potential visitors. The district level centers on route stitching: school routes prioritize safety and playfulness, commuting routes interface and shade, and elderly routes seating and accessibility; since routes cross multiple parcels, a joint cross-parcel governance body could be established and routes projected as renewal units of equal rank with facilities—an institutional proposition that goes beyond the audit evidence and whose coordination feasibility remains to be assessed. The neighborhood level centers on staying conditions: equip micro-scale community spaces—entrances, corners, and living streets—with seating, shade, lighting, and play elements as a micro-renewal menu; open the north entrance of the neighborhood park to shorten the near-yet-far detour; and such projects dovetail with existing policy channels of old-community retrofitting and complete-community building and can be phased into annual programs.

Implementation proceeds in two cycles: a screening cycle that selects representative elements from current inventories and the local spectrum and completes audit and quadrant classification, and a review cycle in which encounter-constrained elements re-examine entrances, routes, and sightlines; quality-constrained elements re-examine need dimensions; and dual-constrained elements re-examine both axes, with results fed into the annual indicators of urban physical examination. Two biases must be avoided in renewal: clearing away residents’ self-made staying points and everyday relations in the name of tidiness, and substituting formalistic participation for residents’ substantive influence on renewal choices [44]. Optimizing an old city is not about making spaces new; it is about connecting the daily life that residents already live into the spaces planned, which has long been overlooked.

6. Conclusions

Addressing the tendency of living-circle planning to weigh facility provision over need verification, this study proposes a three-link framework of perceptual elements, encounterability, and perceptual affordance, decomposing the conversion from spatial supply to need fulfillment into three separately measurable links—availability, reach-and-visibility, and need fulfillment—and completes a full test in Xi’an’s old city across the city, district, and neighborhood levels, from need translation through dual-axis audit to gap diagnosis.

Three conclusions emerge. First, the spatial carriers of perceptual needs far exceed facility inventories. Translation from public documents shows six needs landing through 18 carriers on 32 audited element categories; informal spaces such as entrances and corners carry the most frequent basic needs; imagery elements such as mountains and commemorative spaces carry the enriched advanced needs; and educational venues, public centers, landscape nodes, and commemorative spaces constitute the old city’s high-perception elements. Second, under conditions of comparatively rich provision, the binding gaps lie at the encounter and support links. Mean encounterability is close across the three levels (2.85–3.18) while mean perceptual affordance diverges (2.60–3.24). Nearly half the city-level categories are encounter-constrained; the neighborhood level has no synergy category and more than half are quality-constrained; the cross-level difference in synergy share is significant (p = 0.007); and the three levels form the resource–encounter, node–route, and frequency–support mismatches, respectively. Third, gap types correspond to need tiers. Basic needs fail on quality, and advanced needs on encounter and interpretation, while the high-scoring carriers of intermediate needs are mostly beautiful but rarely met; the intervention logic follows retrofitting for basic needs, opening for intermediate, interpretation for advanced, and the inversion between design investment and use intensity should correct the ordering of renewal resources.

Relative to prior research, the contribution is three extensions: of evaluation objects, from public facilities to the full spectrum of facilities, travel environment, and public space; of encounter modes, from reach alone to reach and visibility together; and of evaluation output, from composite ranking to gap localization with tiered actions. The framework’s need structure, scoring anchors, and four-quadrant diagnosis are designed to be transferable, while the element spectrum must be rebuilt from local public documents; their validity beyond the historic-city context, however, remains to be established through application in other cities. A single short-cycle audit is embedded in living-circle assessments and urban physical examinations, answering what provision indicators cannot.

This study has boundaries. First, the spatial audit measures the supportive potential of environments and cannot substitute for residents’ satisfaction or actual use; availability itself was treated as a contextual condition of the resource-rich old city rather than as a third audited axis, so the findings concern the conversion of existing supply into experience, conditional on provision, rather than the sufficiency of provision itself. Second, the audit is most effective for basic and intermediate needs, whose supports are visible in physical settings; aesthetic, emotional, and humanistic experience also unfold through seasonal change, times of day and year, and community events such as festivals and celebrations, which a synchronic audit cannot capture, and the advanced tier of spiritual and cultural needs ultimately calls for interpretive qualitative approaches—grounded theory built on prolonged engagement; discourse analysis; and, for deeper readings, phenomenological hermeneutics—beyond auditing alone. Third, the three levels are represented by one nested unit each within a single historic old city, and the audited object sets differ by level, so cross-level contrasts mix scale effects with composition effects; testing scale effects properly would require replicated districts and neighborhoods drawn from different geographical areas and city types. Fourth, the data are cross-sectional and cannot yet trace the evolution of gaps, and the audit applies uniform need weights, without differentiating perceptual priorities across age or social groups. Future research may accordingly validate audit results against resident evaluation and behavioral observation, deploy the qualitative methods above to reach the experiential depth that auditing cannot, rebuild spectra and compare mismatch structures across replicated units and city types, and extend the provision-to-experience evaluation chain to a broader range of settings. Subject to such validation, the framework can provide quantitative support for human-centered urban design and the regeneration of historic neighborhoods.