crankshaft/pg/doc/05_cdb_union_adjacent.md

Union Adjacent

This is an aggregate function that will take a set of polygons and return a geometry array of regions where the polygons are continuous. Basically it combines polygons which are touching in to single polygons.

It takes a single value:

• geometry a list of geometries to be clustered and joined

and returns

• geometry[] an array of the joined geometries.

An example usage would be something like:

  with joined_polygons as (
    select cdb_union_adjacent(the_geom) regions from some_table
  )
  select unnest(region) the_geom from joined_polygons

which will produce a table with regions of continuous polygons from the original table.