I have a large GeoJSON file with a single very complex MultiPolygon, and I would like to turn it into an identical file with many small polygons.
How can I do this? I can use ogr2ogr or mapshaper or PostGIS, or any other command-line tool.
This is what my file looks like:
As OP figured out, the ST_Dump function from PostGIS is one way to explode multipart geometries to single ones:
When the input geometry is a collection or multi it will return a record for each of the collection components, ... .
ST_Dump is useful for expanding geometries. ... . For example it can be use to expand MULTIPOLYGONS into POLYGONS.
SELECT sometable.field1,
(ST_Dump(sometable.the_geom)).geom AS the_geom
FROM sometable;
The following is a related post with Python alternatives: Converting huge multipolygon to polygons
To convert multipolygons to polygons with ST_Dump
CREATE TABLE polytable AS
SELECT
id, (ST_Dump(w.geometry)).geom::geometry(Polygon,25833) AS geom
FROM
table_multi w
CREATE TABLE polygon_table AS SELECT id (ST_Dump(geom)).geom::geometry(Polygon,27700) AS geom FROM multipolygon_table. – Richard Jan 08 '19 at 21:20