Firstly, we need volunteers to trace the features of an area of interest. Using aerial photographs as a backdrop, we can literally trace road networks, buildings and landmarks to build a line drawing of the area.
Next, we need people on the ground to collect the local names of neighbourhoods, roads, buildings, lakes, etc. This can be done by physically taking printed copies of maps created in step one, or by data collection on GPS devices or smartphones, and checking this information locally.
Lastly, MSF and other humanitarian organisations can start using the mapped information in outbreak management, epidemiology, logistics and other activities that save lives.
The first stage of this process can be done by anyone, from anywhere with some dedication and training. You just need to sign up to OpenStreetMap and spend some time learning how to use the software. Once you are comfortable, you can start!