Understanding spatial relationships between determinants and outcomes of health care is important as the concept of population-based health care gains acceptance. A wide range of tools for understanding these spatial relationships is available to the family medicine researcher through the use of Geographic Information Systems (GIS). The power of GIS lies in its ability to display the spatial distribution of a health related predictor or outcome. These maps can then be used to either generate or test hypotheses that would not have otherwise occurred to the investigator without visualizing the spatial relationships. The type of GIS application used is dependent on the type of data the researcher has and the research question. The three most common types of data are point or event data, lattice data, and geostatistical data.