It's from the Training Manual Richard: https://docs.qgis.org/2.14/en/docs/training_manual/spatial_databases/spatial_functions.html Apologies if there is something more recent, if there is I couldn't find it. Regards, Nick. -- Sent from: http://osgeo-org.1560.x6.nabble.com/QGIS-User-f4125267.html