A geographical information system was developed to monitor and analyze mosquito abundance and encephalitis virus activity in the Coachella Valley to facilitate mosquito control operations. Data layers include soil types, vegetation types, irrigation method, standpipes, larval occurrence, adult abundance, and viral transmission to sentinel chickens. Base maps are digitized aerial photographs, with data entry done through sections of the range/township system. The image resolution of a section is 100 ft2 (9.3 m2) per pixel. This system currently is operational and in use by the Coachella Valley Mosquito and Vector Control District for data management.