Round 1

Reviewer 1 Report

The authors have proposed a method for the identification of urban functional regions by leveraging online taxi hailing traffic data, decomposing it, clustering it, and studying these clusters. 

Overall I think the paper is interesting and well written. Most of the methodologies adopted are well-reasoned. Figure 7 needs more explanations. One way to present the final findings could be to overlay the 8 identified regions on a map of the underlying region.

Author Response

Response to Reviewer 1 Comments

Point 1: Overall I think the paper is interesting and well written. Most of the methodologies adopted are well-reasoned. Figure 7 needs more explanations. One way to present the final findings could be to overlay the 8 identified regions on a map of the underlying region.

Response 1: We appreciate the reviewer for the valuable suggestions. We explained more about Figure 7 (now Figure 9) to further illustrate the characteristics of each cluster in time (see lines 457-486 on page 15). Actually, the spatial distribution of the final findings is the same as Fig 8(e), but the only difference lies in the functional identification of each Cluster. Therefore, to avoid duplication, we think it may not be necessary to make a new overlay map.

Author Response File: Author Response.docx

Reviewer 2 Report

Dear Authors,

thank you for very interesting article.

Please find attached a file wit my small remarks.

Comments for author File: Comments.pdf

Author Response

Response to Reviewer 2 Comments

Point 1: For formula 4: In the whole of article you use to denote the variable simple font, not italics. I recommend to unify the records.

Response 1: We appreciate the careful read of the reviewer, and revised the writing issues pointed out by the reviewer. Besides, we checked the whole manuscript to improve the writing.

Point 2: For references: The literature review should be expanded on positions prepared by authors from other part of world.

Response 2: We appreciate the valuable comments of the reviewer. We further revised the literature review, and separated it out as Section 2 (Related Works), and revised the literature for the introduction to improve the richness and regional diversity of the literature.

Author Response File: Author Response.docx

Reviewer 3 Report

Language of the manuscript-at-hand needs to be revisited, i.e., particularly, in terms of the sentence structure and the punctuation.

Line 57 -> The notion of 'big data in cities' needs to be delineated in detail. What short of data is there? What are the characteristics of such data? What is its impact?

Line 74 -> The notion of 'online car-hailing' has been introduced for the first time in the section, Introduction, and needs to be illustrated in-depth here.

The contributions of the manuscript-at-hand needs to be delineated at the end of the section, Introduction, in a sequential manner, i.e., as (1), (2), and (3), or as (i), (ii), and (iii). This should be further followed by the structure of the manuscript-at-hand, i.e., a short paragraph outlining the salient features of each Section (flow of the manuscript) is indispensable here.

I would also suggest introducing a section, Related Work, which introduces existing state-of-the-art in terms of their pros and cons. The research gap addressed in this manuscript should, in fact, logically originate via the same.

A Table summarizing the symbols used in the Mathematical Models should be introduced in Section 3, Methodology, too.

Author Response

Response to Reviewer 3 Comments

Point 1: Language of the manuscript-at-hand needs to be revisited, i.e., particularly, in terms of the sentence structure and the punctuation.

Response 1: Thanks to the reviewer's suggestions, we have made further touch-ups and revisions to the manuscript in order to improve the quality.

Point 2: Line 57 -> The notion of 'big data in cities' needs to be delineated in detail. What short of data is there? What are the characteristics of such data? What is its impact?

Response 2: We appreciate the valuable comments of the reviewer. We defined the notion of 'big data in cities' in the introduction section (see lines 56-62 on page 2). In addition to inheriting the “5Vs” (volume, velocity, value, variety and veracity) of big data, big data in cities has the attributes of time and space, indicating human movements, spatial interactions and human-land relationships. We further introduced the online car-hailing data related to our paper in more details in the related works section (see lines 115-136 on page 3).

Point 3: Line 74 -> The notion of 'online car-hailing' has been introduced for the first time in the section, Introduction, and needs to be illustrated in-depth here.

Response 3: We appreciate the reviewer for the valuable suggestion. We made a in-depth illustration of the notion of 'online car-hailing' (see lines 76-84 on page 2) and further introduced the online car-hailing data in Subsection 2.1.

Point 4: The contributions of the manuscript-at-hand needs to be delineated at the end of the section, Introduction, in a sequential manner, i.e., as (1), (2), and (3), or as (i), (ii), and (iii). This should be further followed by the structure of the manuscript-at-hand, i.e., a short paragraph outlining the salient features of each Section (flow of the manuscript) is indispensable here.

Response 4: We appreciate the valuable comments of the reviewer. We added the contributions of this manuscript at the end of the introduction section (see lines 97-104 on page 2 and page 3), and presented a brief summary of each Section following it (see lines 109-113 on page 3).

Point 5: I would also suggest introducing a section, Related Work, which introduces existing state-of-the-art in terms of their pros and cons. The research gap addressed in this manuscript should, in fact, logically originate via the same.

Response 5: We appreciate the valuable comments of the reviewer. We further revised the literature review, and separated it out as Section 2 (Related Works), and presented current research conducted using online car-hailing data, as well as current research on urban functional zoning in Section 2.

Point 6: A Table summarizing the symbols used in the Mathematical Models should be introduced in Section 3, Methodology, too.

Response 6: We appreciate the reviewer for the valuable suggestions. We made a table (see Table 1 at page 4 and page 5) to describe these mathematical symbols used in this paper.

Author Response File: Author Response.docx

Reviewer 4 Report

In this article, the authors provides a new potential perspective for the identification of urban functional zones, which may lead to a better understanding of the urban spatial structure and even urban planning. However, I will comment on some aspects to improve the quality of the manuscript, and the suggested changes made must be highlighted by the authors.

-The acronyms are incorrectly written. The correct form is as in line 21. This error must be fixed in all acronyms that have been used in the article.

-The Introduction Section must be separated into an Introduction Section and a Related Works Section.

-Section 2 must not be in the article. Although the authors add it in some Section or it is eliminated.

-The authors must present a brief summary of each Section that the article will have, at the end of the Introduction Section or Related Works Section.

-The steps presented in Subsection 3.1 must be represented with an Algorithm.

-There are several acronyms that do not have their corresponding meaning.

-Authors must change the word "formula" for Equation.

-Authors must add a brief introduction in Subsection 3.3, 4.1

-The authors must add a Figure only with the scenario that is being studied.

-The link on line 275 must be removed.

-What is the reason for selecting the data for November 16? Is there any previous study to know why it was chosen?

-Figure 1, there are two Subfigures, which have not been separated and do not have their respective separate titles.

-The arrows that go from Figure 1a to 1b have no meaning.

-Figure 1 must have its corresponding geographic coordinate axes.

-In line 327, it is not Section, it is Subsection.

-Authors must avoid the use of Phrasal Verbs in a scientific article.

-How can you observe the aforementioned "grid" if there is no Figure that is large and specifies them?

-What is the measure of each representation of the grid in the study performed?

-The authors must improve the conclusions.

Author Response

Response to Reviewer 4 Comments

Point 1: The acronyms are incorrectly written. The correct form is as in line 21. This error must be fixed in all acronyms that have been used in the article.

Response 1: We appreciate the careful read of the reviewer, and revised the writing issues pointed out by the reviewer. Besides, we checked the whole manuscript to improve the writing.

Point 2: The Introduction Section must be separated into an Introduction Section and a Related Works Section.

Response 2: We would like to thank the reviewer for the valuable suggestions. We revised the Introduction Section, separated out the literature review as Section 2 (Related Works), and presented current research conducted using online car-hailing data, as well as current research on urban functional zoning in Section 2.

Point 3: Section 2 must not be in the article. Although the authors add it in some Section or it is eliminated.

Response 3: We thank the reviewer for valuable comments. We removed the former Section 2 from the article.

Point 4: The authors must present a brief summary of each Section that the article will have, at the end of the Introduction Section or Related Works Section.

Response 4: We appreciate the reviewer for the valuable suggestions. We presented a brief summary of each Section at the end of the Introduction (see lines 109-113 at page 3).

Point 5: The steps presented in Subsection 3.1 must be represented with an Algorithm.

Response 5: We appreciate the valuable comments of the viewer. We revised the main steps to present the basic principle of the EEMD method in the form of algorithm. To have a better effect, we added a flowchart (see Figure 2 at page 6) to represent the specific process of algorithm operation.

Point 6: There are several acronyms that do not have their corresponding meaning.

Response 6: We appreciate the careful read of the reviewer, and revised the writing issues pointed out by the reviewer. Besides, we checked the whole manuscript to improve the writing.

Point 7: Authors must change the word "formula" for Equation.

Response 7: We would like to thank the reviewer for the careful reading. This word "formula" is now replaced by "Equation" (see lines 233 at page 6).

Point 8: Authors must add a brief introduction in Subsection 3.3, 4.1.

Response 8: We added a brief introduction in Subsection 3.3, 4.1 respectively (see lines 239-243 at page 7 and lines 281-283 at page 8).

Point 9: The authors must add a Figure only with the scenario that is being studied.

Response 9: We thank the intensive suggestions of the reviewer. We added a figure to illustrate the scenario studied in this paper (see Figure 1 at page 3). In this figure, we firstly presented an example of the city space and trajectory data. After the spatial aggegration, the traffic time series and periodic decomposition can be obtained. Then the contribution of multi-periodic signals can be calculated and be used for spatial clustering and function identification. Finally, the identification results of urban functional zones are derived.

Point 10: The link on line 275 must be removed.

Response 10: We thank the comments of the reviewer. We revise this sentence. The link is now deleted (see line 294 at page 8).

Point 11: What is the reason for selecting the data for November 16? Is there any previous study to know why it was chosen?

Response 11: We thank the intensive comments of the reviewer. In our case, we selected the data for November 2016. The reasons are as follows: (i) The study area is the central area of Chengdu, which is well developed in 2016, has not changed much, which means that our research based on that data is still indicative. (ii) Our article focuses on the methodology and the data used is only used as a case study for validation. Hence, we think that it is still appropriate to select the data for November 16.

Point 12: Figure 1, there are two Subfigures, which have not been separated and do not have their respective separate titles.

Response 12: We revised the Figure 1 (now Figure 3 at page 9) to more clearly separate the two subfigures. For subplot (a), it is made to present the location of the study area. For subplot (b), we added the title for it: “Traffic volume time series in grid145/147”.

Point 13: The arrows that go from Figure 1a to 1b have no meaning.

Response 13: We would like to appreciate the intensive comments of the reviewer. The arrows indicate that subfigure (b) is a further illustration of the area of grid 145 and grid 147 within subfigure (a). Subfigure (b) shows the 24-hour series of online car-hailing traffic for two representative grids in the study area in subfigure (a). We have bolded the areas 145 and 147 in subfigure (a) and changed the color of the arrows from black to red to enhance the visual effect of this connection.

Point 14: Figure 1 must have its corresponding geographic coordinate axes.

Response 14: We modified the Figure 1 (now Figure 3) by increasing the font size and boldness to show the corresponding geographical axes more clearly.

Point 15: In line 327, it is not Section, it is Subsection.

Response 15: We appreciate the careful read of the reviewer, and revised the writing issues pointed out by the reviewer. Besides, we checked the whole manuscript to improve the writing.

Point 16: Authors must avoid the use of Phrasal Verbs in a scientific article.

Response 16:  We appreciate the valuable suggestions of the reviewer. We have made further touch-ups and revisions to replace the use of phrasal verbs.

Point 17: How can you observe the aforementioned "grid" if there is no Figure that is large and specifies them?

Response 17: The grids are numbered 1, 2, 3, ..., 225 based on the order from left to right and bottom to top. For example, the grid in the lower left corner of the diagram is numbered 1, the grid to its right is numbered 2, and the grid in the row above it is numbered 16.

Point 18: What is the measure of each representation of the grid in the study performed?

Response 18: We thank the intensive comments of the reviewer. The grid is used as the basic spatial unit for signal resolution and spatial clustering analysis. The periodic characteristics of the traffic flow on each grid are measured on it. Based on the similarity of the periodic characteristics, different grids can be combined to obtain a comprenhensive partition.

Point 19: The authors must improve the conclusions.

Response 19: We thank the valuable suggestions of the reviewer. We revised the conclusions to improve the quality. Firstly, since we included the corresponding discussion in the conclusion, we added the "discussions" in the title. We revised the introductory section of the conclusion to better demonstrate the context and significance of the study (see lines 573-577 at page 18). After that, we reorganized the conclusions found in this study, ordering them in a sequential manner. Finally, we discussed the future work in this research area, which is also listed in order.

Author Response File: Author Response.docx

Round 2

Reviewer 3 Report

Thank you for addressing the comments. The overall quality of the manuscript-at-hand has considerably improved.

Reviewer 4 Report

Thanks to the authors for performing the suggested changes. Before publication, a minor check spell is required in the manuscript.