NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competences and with regard for appropriate balance.

The opinions, findings, and conclusions or recommendations contained in this document are those of the authors and do not necessarily reflect the views of the sponsors (the National Science Foundation, the Department of Interior U.S. Geological Survey, the National Geographic Society, and the Association of American Geographers). Mention of trade names or commercial products does not constitute their endorsement by the U.S. government. Supported by the National Science Foundation under Grant No. BCS-0631200; by the Department of Interior U.S. Geological Survey under Award No. 07HQGR0157; and by the National Geographic Society under Award No. 2007-0923.

Library of Congress Catalog Number: 2010926480

Cover: Nighttime lights of the world, courtesy of the National Oceanic and Atmospheric Administration.