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.

This study was supported by the National Aeronautics and Space Administration Award No. W24736; U.S. Department of Agriculture Award No. 59-0790-3-194; U.S. Department of Health and Human Services/Centers for Disease Control and Prevention Award No. 200-2000-00629, Task Order No. 18; and U.S. Environmental Protection Agency Award No. 4W-3838-NALX. Any opinions, findings, and conclusions or recommendations contained in this document are those of the authors and do not necessarily reflect the views of the agencies that provided support for the project. Mention of trade names, commercial products, or organizations does not constitute their endorsement by the sponsoring agencies.

Cover: A choropleth map showing levels of poverty in northern and western Kenya fades into a satellite image showing the color of the Earth’s surface in northern Tanzania. Kenya poverty gap index map courtesy of the Center for International Earth Science Information Network (CIESIN), Columbia University. Satellite imagery courtesy of NASA.