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Millennium Ecosystem Assessment
Uploaded on Tuesday 21 Feb 2012
Urban, dryland, and polar systems
Philippe Rekacewicz, Emmanuelle Bournay, UNEP/GRID-Arendal
Urban systems are built environments with a high human density. For mapping purposes, the MA uses known human settlements with a population of 5,000 or more, with boundaries delineated by observing persistent night-time lights or by inferring areal extent in the cases where such observations are absent.