Within the past few years, passive GPS data loggers have been introduced within the travel behavior research community to collect detailed data on individuals' travel patterns, including the origin and destination of trips, the route taken, the total travel time, and second-by-second speed information. Researchers within the physical activity arena are also beginning to see the benefits of using these passive loggers to collect similar data that can be used for physical activity space and activity level measurement and analysis. The Wearable GeoStats GeoLoggerTM is a passive GPS logger that is self-powered, easy to wear, and capable of collecting detailed location, time, and speed data for weeks between downloads. Longer data collection periods, such as a week, help to reduce the variability of activities measured. These data can then be evaluated within a Geographic Information System (GIS) that, in turn, enables a full spatial and temporal analysis of the GPS data collected by study participants. GIS provides the ability to relate the observed activity of the study participant to the world around him (sidewalks, roads, buildings, trees, slopes, etc.). In addition, GIS provides the ability to analyze the observed activity for the potential of activity by identifying space-time accessibility (e.g., where could I be within a ten-minute walk time?) (Hagerstrand, 1970; O'Sullivan et al., 2000). Finally, by collecting physical activity data from the study participants, such as from an accelerometer (i.e., activity monitor) or pedometer, the intensity of activities can be evaluated within the context of space, time, and environment. In all of these scenarios, GPS data provided by the GeoLogger is the common link that allows for spatial quantification and analysis of physical activity.Keyword(s): community-based programs, measurement/evaluation, physical activity