Vector and Raster Data Models

Every geographic information system rests on a basic choice of how to digitally represent the physical world, and the two dominant answers are the vector and raster data models. The vector model represents discrete features as geometric primitives defined by x/y (and sometimes z) coordinates: points for features such as wells or bus stops, lines for features such as roads or rivers, and polygons for features such as parcels or lakes, each carrying an associated attribute table of descriptive data linked by a unique identifier. This model excels at representing objects with clear boundaries and at storing precise coordinate geometry compactly, and it supports topological relationships — adjacency, connectivity, containment — that let a GIS answer questions such as which parcels share a boundary or which road segments connect at an intersection. The dominant vector interchange format for decades has been the Esri shapefile, documented in the "ESRI Shapefile Technical Description" white paper of July 1998, which stores a single feature layer across a mandatory set of at least three files: a .shp file holding the geometry, a .shx index file, and a .dbf file holding attributes in dBASE table format; the more modern, human-readable GeoJSON format, standardized by the Internet Engineering Task Force as RFC 7946 in 2016, has since become the preferred exchange format for web-based mapping.