A geographic information system (GIS) is a computer system for capturing, storing, checking, and displaying data related to positions on Earth’s surface. GIS can show many different kinds of data on one map, such as streets, buildings, and vegetation. This enables people to more easily see, analyze, and understand patterns and relationships.
The two major types of GIS file formats are raster and vector. Raster formats are grids of cells or pixels. Raster formats are useful for storing GIS data that vary, such as elevation (as seen on this gorgeous Martian landscape map).
Vector formats are polygons that use points (called nodes) and lines. Vector formats are useful for storing GIS data with firm borders, such as school districts or streets.
Long before digital data, cartographers were compiling pre-GIS maps like John Snow's legendary map of the cholera epidemic in London. Cutting-edge geographic information systems still rely on similar cartographic and table or spreadsheet data.