Measuring urban economic density

At the heart of urban economics are agglomeration economies, which drive the existence and extent of cities. This paper estimates urban agglomeration effects, exploring simple and very nuanced measures of economic density to explain household income and wage differences across cities in six Sub-Saharan African countries. A key aspect of the work is that we define cities consistently across space based on fine scale density measures, in order to gauge the economic extent of the city. The evidence suggests that more nuanced measures of density, which attempt to capture within-city differences in the extent of clustering, do no better than a simple density measure in explaining income differences across cities. However, total population is a poor measure. We find large wage gains to being in denser cities in Sub-Saharan Africa, generally larger than such estimates for other parts of the world. We also find extraordinary household income gains to density that are far greater than wage ones. Such gains help explain the pull forces driving rapid urbanization in the region.