What is Spatial Data?
Spatial data, or GIS data, is information about the location of features on Earth. There are two main types:
Represented by points, lines and polygons (Figure 1). Formats include TAB (Mapinfo), Shapefiles (ArcGIS), Spatial Data Frame in R, GeoJSON and a range of others. The Shapefile is a widely used format and it consists of groups of the following files:
- .shp – stores the actual geometric shapes (points, lines, polygons)
- .shx – stores the indexes of shapes for fast searching
- .dbf – stores the attributes of each shape (such as names, data source, sometimes coordinates, associated climatic data etc.)
- .prj – the coordinate and projection information. This file only appears once the data has been projected.
Many GIS software and code packages (such as R) have their own spatial data formats, but can import and export Shapefiles. It is for this reason that the Shapefile format is widely used.
Figure 1: Example of vector data (in this case composed polygons)
Made up of pixels or cells that have values associated with them (Figure 2) – also known as grid or bitmap data – often in a photographic or image file format e.g. GeoTIFF, JPEG, BMP or IMG.
Next educational blog: Understanding datums, projections, co-ordinates and co-ordinate Systems.
Written by: Tamra Chapman – Senior Ecologist