A Fine-Grain Multi-Indicator Analysis of the Urban Form of Five Informal Settlements in East Africa
Abstract
:1. Introduction
2. Methodology
2.1. Acquisition of Spatial Data
2.2. Field Interviews
2.3. Indicators of Urban Form
- Block size (BS) corresponds to the total area of each block;
- Coverage ratio (CR) quantifies the percentage of land which is occupied by buildings in each block. It is computed by multiplying the sum of the building footprints in each block by 100 and by dividing this value by BS;
- Floor area ratio (FAR) measures the built-up density of the block. It is calculated by summing up the gross floor areas (GFAs), obtained by multiplying building footprints by number of floors, of each building pertaining to the block and by dividing such value by BS;
- Surface area to volume ratio (SAV) quantifies the level of fragmentation of the building envelopes in each block. Typically, a simple box-shaped building would have a small SAV, as it is compact and thus does not have any protruding parts or cavities. On the contrary, a complex building with many recesses and/or protruding elements would have a greater SAV. This indicator is largely used in studies focusing on the energy efficiency of buildings. See, for example, the work by Ratti et al. [13]. SAV is computed by multiplying the perimeters of the buildings in each block by their relative heights, summing two times the sum of the building footprints in each block to this value, and by dividing this sum by the total built-up volume in each block;
- Average node degree (AND) measures the level of connectivity at the block level. It is computed by averaging the node degrees relative to the street intersections surrounding each block. In practice, a block surrounded by many dead-end streets (i.e., node degree equals 1) would have a low average node degree and thus low local connectivity. Conversely, a block surrounded by several four-way intersections (i.e., node degree equals 4) would have a greater average node degree and thus higher local connectivity. Node degree is a widespread measure of network connectivity used, for example, in social networks [14] and communication [15].
- Average betweenness at 400 m (AB400) measures through movement in street networks. It was reported to correlate with several urban phenomena such as concentration of commerce and services [16], employment density [17], and street quality [18]. The formula of betweenness centrality [19] can be adapted to output levels of through movement at different urban scales (e.g., neighbourhood, district, or city region). Since the settlements under examination have sizes comparable to that of city neighbourhoods, we computed betweenness centrality on their street networks with a radius of 400 m, a measure typically associated with the neighbourhood scale [20]. Finally, each block was assigned with the average value of betweenness centrality of its surrounding streets.
- Private space ratio (PrSR) quantifies the amount of private space relative to the built-up density. It is computed by subtracting the sum of building footprints from BS and by dividing this value by the sum of the gross floor areas (GFAs) of each building within the block.
- Public space ratio (PuSR) measures the amount of public space relative to the built-up density. The amount of public space in each block is obtained by subtracting BS from the area of the polygon enclosed by the road centre lines surrounding each block. PuSR is computed by dividing such value by the sum of the gross floor areas (GFAs) of each building within the block.
2.4. Statistical Comparison
3. Case Studies
4. Results
4.1. Field Interviews
4.2. Settlement Characteristics, Similarities, and Differences
5. Discussion
6. Conclusions
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
Appendix A
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Antohomadinika | Hananasif | Katanga | Kibera | Maxaquene | Average | |
---|---|---|---|---|---|---|
N. interviewees | 10 | 10 | 10 | 10 | 10 | 10 |
Tenants (%) | 70.00 | 40.00 | 90.00 | 90.00 | 0.00 | 58.00 |
Cost of rental household (USD/month) | 11.14 | 17.20 | 27.12 | 40.15 | - | 23.90 |
Dwelling size (rooms) | 1.60 | 4.40 | 1.10 | 1.30 | 4.40 | 2.56 |
Household size (people) | 3.90 | 9.40 | 4.00 | 4.90 | 6.30 | 5.70 |
People per room (people/rooms) | 2.44 | 2.13 | 3.64 | 3.77 | 1.43 | 2.68 |
Household access to water (%) | 20.00 | 60.00 | 0.00 | 0.00 | 90.00 | 34.00 |
Household access to sanitation (%) | 40.00 | 100.00 | 0.00 | 30.00 | 100.00 | 54.00 |
Household access to electricity (%) | 90.00 | 90.00 | 80.00 | 90.00 | 90.00 | 88.00 |
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Mottelson, J.; Venerandi, A. A Fine-Grain Multi-Indicator Analysis of the Urban Form of Five Informal Settlements in East Africa. Urban Sci. 2020, 4, 31. https://doi.org/10.3390/urbansci4030031
Mottelson J, Venerandi A. A Fine-Grain Multi-Indicator Analysis of the Urban Form of Five Informal Settlements in East Africa. Urban Science. 2020; 4(3):31. https://doi.org/10.3390/urbansci4030031
Chicago/Turabian StyleMottelson, Johan, and Alessandro Venerandi. 2020. "A Fine-Grain Multi-Indicator Analysis of the Urban Form of Five Informal Settlements in East Africa" Urban Science 4, no. 3: 31. https://doi.org/10.3390/urbansci4030031