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I am importing Polygon shapes into a PostGIS database, using Python (GeoPandas, SQLAlchemy, GeoAlchemy2). I followed the instructions mentioned here.

I have a database with a table named maps_region with a column/field called geom.

I am able to get the Polygon field (named geom) to import into the PostGIS database table in text format (WKT, WKB, and WKB Hex), but, I am unable to successfully convert this text column into a proper Polygon format in the database.

I tried importing with the geom field in several different formats-- in Well-Known Text (WKT) format, WKB format, and WKB Hex format-- but could not convert to Polygon from any of the three formats.

For instance, I imported the shapes into the geom field as WKT format, and then converted to WKB Hex format, using the following command, which worked fine:

database=> UPDATE maps_region SET geom = ST_GeomFromText(geom, 4326);
UPDATE 28

However, when I then try to convert the geom field from a text format into a Polygon type, I get the following errors: 

database=> ALTER TABLE maps_region ALTER COLUMN geom TYPE Geometry(POLYGON, 4326);
ERROR:  Geometry type (MultiPolygon) does not match column type (Polygon)
database=> ALTER TABLE maps_region ALTER COLUMN geom TYPE Geometry(MULTIPOLYGON, 4326);
ERROR:  Geometry type (Polygon) does not match column type (MultiPolygon)

I tried both ways: converting to Polygon, and converting to MultiPolygon-- and neither worked. Instead, the error messages were just reversed!

Any help would be greatly, greatly appreciated.

Thanks in advance!

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briangoodness
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1 Answers1

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I realized that the shapes were being registered in mixed format: all but one were in Polygon format, while one was in MultiPolygon format -- see here. Looks like this sufficiently explains the issue/invalid conversion.

briangoodness
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