The evolution of built-up areas in Ghana since 1975

We use high resolution satellite data on the proportion of buildingsin a 250x250 meter cell to study the evolution of human settlementin Ghana over a 40 year period. We find a strong increase in built-uparea over time, mostly concentrated in the vicinity of roads, andalso directly on the coast. We find strong evidence of agglomerationeffects both in the static sense -- buildup in one cell predictsbuildup in a nearby cell -- and in a dynamic sense -- buildup ina cell predicts buildup in that cell later on and an increase in buildupin nearby cells. These effects are strongest over a 3 to 15 Km radius,which corresponds to a natural hinterland for a population withoutmechanized transportation. We find no evidence that human settlementsare spaced more or less equally either over the landscape or alongroads. This suggests that arable land is not yet fully utilized, allowingrural settlements to be separated by areas of un-farmed land. By fittinga transition matrix to the data, we predict a sharp increase in theproportion of the country that is densely built-up by the middle andthe end of the century, but no increase in the proportion of partiallybuilt-up locations.