OpenStreetMap

OSM Homepage: http://www.openstreetmap.org/

Import

• GRASS_AddOns#v.in.osm (fairly rough script)

Conversion with Mapnik to raster tiles may work, but be very careful about projection issues, typical online web map tiles are not appropriate for GIS import.

Data as shapefiles

Get data from here:

• http://download.geofabrik.de/osm/ ,or
• http://downloads.cloudmade.com/

Then import with v.in.ogr

Data from WMS

• Web Map Service (WMS) for Europe: GetCapabilities to access the WMS
• No free/open world-wide server known - Badly needed

Then import with r.in.wms

OSM vs. GRASS topology

OSM topological model is different to GRASS topological model. OSM topologically correct connections of the lines can be on all nodes of the line. Unlike OSM, GRASS allows to connect lines only on their starting/end nodes.Therefore after the import it is needed to split lines into the smallest segments by "v.split vertices=2". However after application of the v.split, there are too many lines and some of them are not necessary. Module v.build.polylines cats=same merges the extra lines into single polyline.

Corect topological model is necessary e.g. to perform Vector network analysis.

Expample

The following image represents roundabout after the import of the OSM shapefile from geofabrik. You can see that there is only one category number 917. It means that the roundabout circle is just one line and grass does not see all connections to the other lines, because they are not on the starting/end node of the circle.

v.in.ogr output

After the application of v.split it gives too many one segment lines. It is clear form the following image:

v.split output

v.build.polylines merges unnecessary segments. All lines starts/ends on the intersections with other lines as can be seen on the following image:

v.build.polylines output

There is another possibility to use v.clean tool=break but if there is e.g. a bridge then v.clean connects it to the roads going bellow it which is incorrect. The above described approach does not split the bridge there. See the difference on the following images:

Output of v.split -> v.build.polylines

Output of v.clean tool=break

See also

• Extrude 2D polygons to 3D
• Simplifying OSM Shapefiles using GRASS