Combining GPS units with accelerometers is becoming a common method of objectively assessing adult physical activity locations. However, few best practices have been proposed for designing these studies. Using accelerometer and GPS data collected from over 200 adults in five cities, 10+ minute bouts of physical activity were given location codes with a Google Maps-based coding protocol. This data was then used to answer the following questions: “How long do participants need to wear a GPS monitor to reliably identify minutes of physical activity spent in specific locations?” and “Do residential buffers accurately reflect the physical activity spaces of adults?”