Clipping geometries to deploy data

A common GIS use case is clipping a big dataset into small portions (subsets), with maybe each representing an area of interest. In this recipe, you will export from a PostGIS layer representing the rivers in the world one distinct shapefile composed of rivers for each world's country. For this purpose, you will use the ST_Intersection function.

Getting ready

Be sure that you have imported in PostGIS the same river dataset (a shapefile) that was used in the previous recipe.

How to do it...

The steps you need to perform to complete this recipe are as follows:

1. First, you will create a view to clip the river geometries for each country using the ST_Intersection and ST_Intersects functions. Name the view rivers_clipped_by_country:

   postgis_cookbook=> CREATE VIEW chp03.rivers_clipped_by_country AS
       SELECT r.name, c.iso2, ST_Intersection(r.the_geom,c.the_geom)::geometry(Geometry,4326) AS the_geomFROM chp03.countries AS c
       JOIN chp03.rivers AS r
       ON ST_Intersects...