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Assessing risk of informal settlements in Dar es Salaam with OpenStreetMap

Authors: Joseph Holler*, Middlebury College
Topics: Hazards, Risks, and Disasters, Hazards and Vulnerability, Geographic Information Science and Systems
Keywords: OpenStreetMap, Urban Resilience, Disaster Risk Reduction
Session Type: Paper
Presentation File: No File Uploaded


Urbanization in the global South is outpacing formal planning and development to support transportation, water, sewage, energy, and legal property rights, resulting in the proliferation of informal settlements. In the context of urban disaster risk, informal settlements are particularly vulnerable because of their fast growth and change, high exposure to natural hazards, and low capacity to adapt. Humanitarian OpenStreetMap (OSM) and similar platforms are responding to this risk by digitizing missing data through coordinated digital humanitarian volunteering and participatory mapping. OpenStreetMap has provided essential reference maps for crisis areas, but disaster managers question how to better synthesize large amounts of volunteered data into knowledge for decision-making.

I use Dar es Salaam in Tanzania as a case study to illustrate methodology for querying spatial patterns in OSM building footprints to detect the locations and morphology of informal settlements to aid in disaster risk reduction. Dar es Salaam is growing at annual rates exceeding 4 percent while up to 70 percent of its residents live in informal settlements, many of which are situated in flood-prone areas. In support of urban resiliency and risk reduction, the Dar Ramani Huria project trained and mobilized volunteer mappers, drone imagery, and LiDAR to digitize Dar es Salaam's urban landscape in OpenStreetMap. Using building footprints from OpenStreetMap and PostGIS, I derive a set of neighborhood-based indicators of urban morphology to detect informal settlements and quantify their morphology-based levels of risk.

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