GIS data - also called geographically enabled data or geospatial data - comes in a wide variety of formats with one thing in common: a geographic component. That geographic component could be a country name, street address, latitude and longitude coordinates, city name, or anything else that designates a specific spot or area on the surface of the earth. In fact, a spreadsheet of data with a geographic component can almost always be mapped using GIS software.
Datasets in GIS formats can be classified into two broad categories: raster data and vector data.
Raster data is a type of digital image represented by reducible and enlargeable grids or pixels, wherein each pixel has a value. Examples of raster data include air photos (each pixel's value is a colour) and digital elevation models (each pixel's value is a number representing height above sea level). Common file formats include JPEG, GeoTIFF, and MrSID.
Vector data consists of points, lines, or polygons. Examples of vector data include hospital locations (points), roads (lines), and lakes (polygons, which have area). Common vector file formats include shapefiles, Google Earth KML, and AutoCAD drawing files.