Day 20: Tuesday 27 September - Depthmap Analysis of Connectivity in Delmas 19 Target Area

Introduction

Depthmap is a piece of software developed by Space Syntax. It was used to produce a series of ‘visibility graphs’ that display relative amounts of ‘connectivity’ across a given space.

Each location is coloured according to how many locations are visible from it. Areas with high connectivity are visible from many different locations and areas with low connectivity are enclosed and visible from few other locations.

Areas of high connectivity are anticipated to be open, public spaces such as markets and main roads, while low-connected places are expected to correlate with narrow, possibly dark spaces in the centre of the slum.

Methodology

The cadastral survey was used as the input for this analysis. The cadastral survey was imported into ArcGIS as a polygon shapefile with each polygon representing an individual building plot. The spaces between the building plots consist of the corridors and the canal. The editor tool in ArcGIS was used to edit the corridors and the canal to close-off any areas known to be inaccessible. The main roads bordering the site were also linked to each other and incorporated into the analysis. Once the shapefile was edited it was exported to a DXF polyline format and imported into Depthmap.

In Depthmap a grid was created with a 0.25m spacing, which ensured that at least 3 grid-cells fit within the narrowest corridor space. If the grid size had only 1 grid cell representing the width of a corridor the connectivity would unnaturally bottleneck in some areas. The final step of the data preparation stage is to fill the corridors and other accessible areas using the fill tool. These are the areas that the software will apply the analysis to.

Objectives

Visibility graphs were produced for four different scenarios to explore how connectivity would be affected in Delmas 19 if the canal was covered or not. The canal runs through the centre of Delmas 19. It was uncovered before the earthquake, but has been covered half-way using funds from the IOM. The scenarios tested using this analysis include:

Scenario 1: Canal covered half-way (this represents the current status in Delmas 19)
Scenario 2: Canal not covered (this represents the status before the earthquake)
Scenario 3: All canal covered (this represents the status if the rest of the canal is covered)
Scenario 4: Canal covered half-way with 3 central derelict buildings demolished (this represents the current status in Delmas 19 after 3 derelict buildings in the central part of the scene are demolished)

Results

Scenario 1: Canal covered half-way
Scenario 2: Canal not covered
Scenario 3: All canal covered
Scenario 4: Canal covered half-way with 3 central derelict buildings demolished
Summary

The results of the analysis suggest that covering the canal will not change the connectivity in other parts of the site. This is because Delmas 19 is comprised mainly of narrow, bendy corridors - so the change in connectivity brought about by covering the canal is very localised.

What is apparent though is that covering the canal would create a new corridor to the centre of Delmas 19 that is relatively well-connected to other areas. This is due to its direct connectivity to the very open market areas to the south of the scene. Demolishing 3 derelict buildings in the centre of the scene would also create a relatively well-connected space in an otherwise very enclosed area.

Network analysis on the same datasets is likely to show that covering the canal will improve accessibility to the centre of Delmas 19. The t-shaped canal system – if covered – could provide important access to all four Cites from the south, west and east.