Understanding the spatial distribution of small-scale fisheries, a key step toward the formulation of sound management guidelines where these fisheries predominate, represents a challenge, as reliable data for small-scale fisheries is often limited. One way to cope with "data-poor" fisheries is to capitalize on the accumulated local knowledge of fishers as part of the research and management process. We introduce an approach to incorporating fishers' local knowledge at a large, regional scale. We focused on the spatial distribution of fishing activities from 17 communities in the northern Gulf of California, Mexico. Participatory interviews and mapping through rapid appraisal (n = 376 fishers) were used to identify fishing grounds and fishing seasons. A geographic information system was used to generate 769 map layers used for a preliminary analysis of rapid-appraisal spatial data. We organized postsurvey workshops with fishers to facilitate an internal validation of spatial information using geographic information system. These exercises generally resulted in agreement with the general distribution of fishing areas originally mapped but also led to the addition of new areas not registered during the rapid appraisal and important adjustments for some species, particularly in areas where depth contours are pronounced. In all, cross-checking during the validation workshops led to an aggregated increase in total fishing area of 1.08%. Our study provides an example of how key local knowledge can be incorporated into and corroborated during the data-collection process within large, regional scales with multiple fishing communities and highly diverse fishing activities. © 2010 Rosenstiel School of Marine and Atmospheric Science of the University of Miami.