Putting 'invisible' Mathare Valley on the map

If you were to do a search for the Nairobi city slum of Mathare on Google Maps, you'd find little more than gray spaces between unmarked roads.

Slums by nature are unplanned, primordial cities, the opposite of well-ordered city grids. Squatters rights rule, and woe to the visitor who ventures in without permission. But last year, a group of activist cartographers called the Spatial Collective started walking around Mathare typing landmarks into hand-held GPS devices.

In a slum with no addresses and no street names, they are creating a map of what it's like to live here. read more: www.wbur.org/npr