A GIS is a computer system for capturing, storing, analyzing, and managing spatial data referenced to locations on Earth. It has four main components: data, hardware, software, and people. GIS data comes in three types - vector, raster, and attribute. GIS allows for spatial analysis of data patterns, querying data based on user criteria, and producing maps. It is a useful tool across many industries for decision making and planning through its visualization and analysis capabilities of geospatial information.