Research has shown that behaviors and health outcomes are associated with built environment characteristics. However, the majority of research has relied on self-reported, rather than objective data. New approaches use objective methods for measuring physical activity behavior (accelerometry) and location (global positioning systems, GPS), coupled with objective built environment data from geographic information systems (GIS). Coupling accelerometry, GPS, and GIS, allows for investigation of the times and places where physical activity occurs, and quantitative estimation of the duration of exposure to features in the built environment. Brief results from three studies are presented, one that shows that transit users obtain approximately 15 additional minutes of walking physical activity per day on days when they take transit. A second study found that persons residing in neighborhoods with higher Walk Score (R) values engage in more bouts of walking. The third study showed that at locations very close to, or further from home, people obtain less physical activity than they do in locations near the home neighborhood. Combining these objective measurement methods promises to shed light on the complex interrelationships between environment and behavior.