Brazil has 109 million hectares of sustainable use reserves (SURs), most of them in Amazonia. In practical terms, SURs are being created to meet several objectives, but this process can and should be improved. The absence of a clear goal and the lack of basic social and biological information for such areas can compromise the goals, frustrate the people demanding the SURs and complicate the selection of the most adequate size, shape and category to be adopted. The data collection process used in the creation and management of protected areas is often compromised by under-funded environmental agencies, a lack of qualified human resources or the unawareness of accessible, quick, simple and inexpensive geographical methodologies able to facilitate such processes. The dissemination of tools and methods oriented to improve the management of and the decision-making process for protected areas in such adverse scenarios is necessary. Here we describe the execution of a participatory geographic information system (PGIS) to gain information on how human populations are living and using natural resources in the Maues State Forest, an SUR in Brazilian Amazonia. The PGIS allowed data acquisition for 415 families, 444 houses, 597 agricultural and animal-raising areas, 138 fishing sites, 106 hunting sites and 225 extraction sites within a short period of time (<than 20 days) and with accessible costs (<US$ 10,000). We classified and located the activities and points being used, the areas under stronger pressure and the hotspots for conservation, estimating that nearly 30% of the reserve was under direct use by its residents. We discuss the conservation implications of our findings and strongly recommend that the collection and mapping of socio-economic information should be prerequisite before the creation of any SURs in Brazilian Amazonia. (C) 2010 Elsevier Ltd. All rights reserved.