Background:This study stemmed from the preparatory work for the Bartlett,UCL research project Adaptable SuburbsProject Team: Professor Laura Vaughan, Dr Sam Griffiths, ProfessorMuki Haklay, Dr Claire Ellul, Dr Victor Buchli, Ashley Dhanani andDavid Jeevendrampillai ‘Astudy of the relationship between networks of human activity and the changing form of urban and suburban centres through time’
Origin of this study:For the Adaptable Suburbs research project the street networksystem of London has to be reconstructed for four historic periodsand analysed.The question that originated the evaluation of the street networkdata was: ‘Which data sets should we use as the basis for thereconstruction of the historic street network of London?’Three network datasets were available to us for this study: 1. Commercial: Ordnance Survey Integrated TransportNetwork: ITN 2. User Generated: Open Street Map: OSM 3. Reference: Pre-existing Axial Space Syntax Model ofLondon: Axial
Comparison of geographic structure ITN OSM Axial ITN : OSM : Axial ITN : Axial
Comparison of network length and number of segments London wide network (2,900km2) OSM ITN AXIAL Total Length (km) 29,700 26,027 20,039 Number of Segments 718,118 1,213,646 453,562 Surbiton case study network (110km2) OSM ITN AXIAL Total Length (km) 1,456 1,197 1,075 Number of Segments 37,585 58,293 20,637
Space syntax analysis of Surbiton case study network models- Analysed in Depthmap.- Angular segment analysis of choice and integration.- Utilised segment length weighted analysis (Turner, 2007) for road centre line data to compensate for many shorter lines.- Results compared visually as direct comparisons of values are very difficult in such dissimilar network models.
Axial Model ITN Model OSM Model Surbiton - Choice Radius n
Axial Model ITN Model OSM Model Surbiton - Choice Radius 2000m
Axial Model ITN Model OSM Model Surbiton - Integration Radius n
Axial Model ITN Model OSM Model Surbiton - Integration Radius 800m
Topological step depth analysis Topological Step OSM ITN AXIAL Depth Mean 90 197 49 Median 94 204 50 Maximum 197 422 90 Mode 106 224 44
- All models show the same structurgrowth in regards to segments over s-Although with very different numberSegments involved.-Axial model is a simplification of thestructures and road geometry.
Connectivity analysis -ITN and OSM show the same connectiv properties. -Axial model shows very different co structure. -Further evaluation required of conn properties.
Summary ITN – Most reliable and complete data set but it is too detailed for space syntax analysis and therefore must be cleaned to remove extraneous features. Lacks non-road routes through the urban fabric – represents a model of vehicular- accessible network. OSM – Not reliable in its coverage or methods of data creation but it is a very interesting representation of the city as seen through the eyes of those who inhabit the space. Contains features that commercial data does not. Useful as supplementary data. Axial – This is a different entity to the other models. It represents space in a completely different way. A powerful model but extremely time consuming to construct. Questions as to its representation of complex features – not enough
Conclusion Work has to be done to reconcile the underlying model of space and its implicit account of what is meaningful in space with the analytical toolkit of space syntax analysis. -Vital in further developing angular segment analysis. -Integrating street network and built form for holistic analysis of urban structure and function. Analysis raises important questions as to what should be represented and how: pedestrian-only routes, angular changes in street alignment, etc. The question of how we represent the real-world through data is one that must be carefully considered otherwise the analysis that stems from it can be easily undermined