Vector data represents geographic features as discrete geometries — points, lines (polylines), and polygons — defined by ordered coordinate pairs. Each geometry is linked to a record of attributes (name, type, age, depth, etc.), making vector data ideal for features with clear boundaries.
What it is and why it matters
The three core geometry types map naturally onto real-world features:
- Points — sample sites, boreholes, strike-and-dip readings, summits.
- Lines — faults, contacts, rivers, roads, cross-section traces.
- Polygons — geological units, lakes, license areas, watersheds.
Vector is the counterpart to raster data (a grid of cells, used for DEMs and imagery). Vectors are resolution-independent and compact for sharp boundaries, and they support exact geometric operations — buffering, intersection, spatial joins, topology checks — that underpin most GIS analysis. For geology, a vector geological map preserves the precise line of each contact and the polygon of each map unit along with their full attribute tables.
Concrete example
A geological map stored as vector might contain a polygon layer of map units (each polygon tagged with unit_code, lithology, age), a line layer of faults (with fault_type, dip), and a point layer of field observations. Common storage formats include GeoPackage, Shapefile, GeoJSON, and PostGIS geometry columns. Coordinates are meaningless without a defined CRS — e.g. EPSG:4326 (WGS84 lat/lon) or a projected UTM zone.
Common pitfall
Choosing vector when the phenomenon is continuous. Elevation, slope, and temperature vary smoothly across space and are better modelled as raster grids; forcing them into polygons loses information. Conversely, snapping a crisp boundary to a coarse raster grid degrades it. Match the data model to the phenomenon.