A geographic information system (GIS) is software for capturing, storing, analysing and presenting data that has a location attached to it. What separates a GIS from an ordinary database is that it understands space: it can answer questions about distance, containment, adjacency and overlap rather than only about values.
What a GIS actually does
The core capability is spatial query and analysis — finding what falls inside a boundary, what lies within a given distance, where two datasets intersect, or how a value varies across an area. Around that sit data management, cartography and visualisation.
Vector and raster
GIS data comes in two broad forms. Vector data represents discrete features as points, lines and polygons — a shop, a road, a boundary. Raster data represents continuous surfaces as a grid of cells, such as a digital elevation model or satellite imagery. Most real analysis combines both.
Common tools
ArcGIS is the dominant commercial platform; QGIS is the established open-source alternative. PostGIS adds spatial types and operations to PostgreSQL, which is how much production spatial analysis is actually run.
GIS and location intelligence
GIS is the toolset; location intelligence is what an organisation does with it — turning spatial analysis into commercial decisions about where to open, where to advertise and where demand is moving.
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