Demography. Base demographic data on cities were taken from GRUMP (4,
31). GRUMP urban extents are spatially defined primarily on the basis of
satellite imagery of night-time lights. The extents are then linked with information
from censuses and gazetteers containing population information
on hundreds of thousands of urban settlements, including those with quite
small populations. The algorithm that defines urban extents, especially for
large urban agglomerations, typically gathers contiguous urban and suburban
areas into one urban extent. For our study, we evaluated the water
availability and population for the entire urban extent as measured by
GRUMP; this assumes water sharing among constituent municipalities that
may or may not occur in practice.