At HOT, we are working on a collaboration with communities in informal settlements in Sierra Leone as part of the Know Your City project led by Slum Dwellers International.

The remote mapping of the settlements is hard, even with the excellent drone imagery flown by OpenStreetMap Sierra Leone. The environment is really dense, roofs overlap at different heights and structures that look like one from the sky actually include multiple buildings.

However, we have found the use of 3d and 2d imagery renders in parallel to be a bit of a game changer for this mapping activity. The mesh produced from the drone images allows us to angle and tilt in a way that we can better see how roofs interact with each other, what height they are and even sometimes how buildings are divided inside. We think this has vastly improved the accuracy of what we are able to do remotely.

3d mesh of Kolleh Town, Freetown, Sierra Leone

The mapped area on OpenStreetMap

The remote mapping will be followed by comprehensive field mapping and surveying by the local community and the team at CODOHSAPA using the Field Mapping Tasking Manager, so it is important to get the basemap as accurate as possible.

A big thanks to OSM Sierra Leone for their support and collaboration on this project as well as our partners at SDI, CODOHSAPA, Freetown City Council and Catholic Relief Services.