Figure 3. Partitioning of countries based on telephone call networks.

(A) Ivory Coast and (B) Saudi Arabia. The black lines show the 19 and 13 administrative regions, respectively, the colored areas show the corresponding 11 and 12 level 1 regions found by applying the modularity optimization algorithm on the country-wide phone call networks. For these two countries, the matching shows less overlap than for other countries, likely due to the low population density and the sparse data. Almost all detected subregions are cohesive, exceptions appear in Saudi Arabia which is very heterogeneously populated. Due to the heterogeneous distribution of cell towers, a second level partitioning is not feasible here.