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Taking some OSM (*.osm) data downloaded from Geofabrik I have created a Spatialite database using spatialite_osm_map. Now I have problems, because some of the data that is supposed to be in the form of polygons appears in the database as polylines, which I can't style properly. As an example, objects tagged "natural=wood" appear correctly as polygons in the DB while objects tagged "landuse=forest" appear as lines.

I think this must be something to do with what I've seen called the "multipolygon problem". At present I am loading the affected objects into QGIS, exporting them as shapefiles and then polygonising these, but there must be a better way of working. Any help on this topic would be gratefully received.

I ought to mention that what I know about Spatialite and OSM data wouldn't fill a thimble.

Added later: here is a screenshot illustrating the problem. The "polygon" selected by the info tool is in fact a polyline. Nick.

enter image description here

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Can you show the steps to repeat this? It would help to know exactly which data, and exactly how you are running spatialite_osm_map. – BradHards Aug 2 '12 at 9:40
The data is "england.osm" from Geofabrik. To load it into the DB I used "spatialite_osm_map -o england.osm -d enJUL2012.sqlite". Geofabrik's shapefiles also have this problem. Using QGIS Master under Ubuntu 12.04 (amd64). Thanks for your interest. N. – nhopton Aug 2 '12 at 10:54

1 Answer

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In Openstreetmap, polygons can be build either by one closed way, or by a number of ways, which form a closed way. Those ways have to be part of a "relation" of type "multipolygon".

I dont know your tool, but the safest way to have those polygons correctly is to use a Postgis database filled with osm2pgsql.

A sample osm-id from your data could help investigating further.

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Hi Andre, I've added a picture above with an OSM id. N. – nhopton Aug 2 '12 at 11:16
Ok, so its a simple closed way, no recent editing in the database, and no redaction bot involved. Using the OSM plugin within Qgis gives a nice polygon. And the Geofabrik shapefile has the object in layer natural. I dont know what problems the spatialite tool has. – Andre Joost Aug 2 '12 at 11:26
"Closed ways", thanks for the proper terminology. But how to get these into a Spatialite DB as polygons? N. – nhopton Aug 2 '12 at 11:46
Have you tried the Openstreetmap plugin? It creates layers within qgis, which you can copy&paste to your database layers. – Andre Joost Aug 2 '12 at 12:00
I just tried spaitalite-osm-map on the single way I downloaded with JOSM editor. It has been imported as a polygon in pg_landuse as expected. SQLite version 3.7.9, Spatialite version 3.0.1 under Windows 7. – Andre Joost Aug 2 '12 at 15:03
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