Please use the following information when citing the GPW.

Gridded Population of the World, Version 3 (GPWv3)
Citation Information:
Originator: Center for International Earth Science Information Network (CIESIN), Centro Internacional de Agricultura Tropical (CIAT).
Publication Date: 2005
Title: Gridded Population of the World, Version 3 (GPWv3) Data Collection
Geospatial Data Presentation Form: raster digital data, map
Publication Information:
Publication Place: Palisades, NY
Publisher: CIESIN, Columbia University
Online Linkage: http://sedac.ciesin.columbia.edu/gpw/index.jsp

For more information on how to cite our data, please see our Citation Guidelines site at http://sedac.ciesin.columbia.edu/citations/CitationGuidelines.html