PostGIS in Action, Third Edition

8 Spatial relationships

This chapter covers

• Bounding boxes
• Intersections
• Relationships
• The meaning of equality
• The Dimensionally Extended 9-Intersection Matrix (DE-9IM)

As the old saying goes, “No man is an island,” and the same holds true for spatial objects. In prior chapters we described geometries and rasters in isolation. Going forward, we’ll no longer entertain ourselves with one geometry at a time or one raster at a time. The richness and power of spatial queries come to light when you start working with more than a singleton.

If we liken spatial objects to tables, an SQL query that queries a single table can only go so far. It’s when you have join operations at your disposal that things become interesting. Mastering join operations ...