GIS, Remote Sensing and Satellite Navigation

Modern geographers analyze places with layers of digital data. A geographic information system, or GIS, stores maps as layers such as roads, rivers, population and land use, then lets users overlay them to find patterns, for example which homes lie inside a flood zone. The idea of mapping data to reveal causes is older than computers: in 1854 physician John Snow mapped cholera deaths in London and traced many to a single water pump on Broad Street.

Remote sensing gathers information from satellites and aircraft, and the Landsat program has photographed Earth continuously since 1972, making it possible to measure deforestation, urban growth and shrinking glaciers. The Global Positioning System lets receivers calculate position by timing signals from several satellites. These tools raise questions as well as answers: data can be incomplete, and detailed location tracking creates real concerns about privacy.