Populations, megapopulations, and the areal unit problem.

Models of epidemic disease and programs for their management require accurate population data as a critical component of most studies. But the traditional definitions of urban places assumed discrete borders and localized populations. The vast increase in urban travel at all scales has raised the problem of how we define those urban populations. This paper reviews the issues as an areal unit problem within the context of the evolving idea of "megaregions" and their defintion.