Settlements expand and evolve as populations grow. Population size and densities are among
the criteria used to characterize a settlement as either urban or rural. Despite ongoing debate,
there is broad agreement globally that settlements over 20 000 people, and a population density
of over 1 000 people per km2, are urban1. This cut-off does not however reflect the functional
inter-dependence of urban and rural areas, as the new municipal demarcation has recognized.