Playing with OSM data

I’m playing with OpenStreetMap data in PostGIS, drawing maps in QGIS. No serious cartography, mind you, just trying to get a feel for the data. I’m starting with Mike Migurski’s metro extracts, the .osm.bz2 file for San Francisco

Import that into PostGIS, which gives this schema which describes these map features.

osm2pgsql -d walks --style /usr/share/osm2pgsql/default.style san-francisco.osm.bz2

For the SF metro, there’s 8000 roads, 40,000 polygons, 31,000 points, and 62,000 lines. You can import all these tables directly from pgsql into QGIS and render them for a basic view. The lines contain the street grid; roads contains just the larger highways, etc.

QGIS makes it easy to explore the tables. When you add a new PostGIS layer and choose a table, you can then choose specific fields and sample their values. Exploring around you can find that “leisure=park” is an interesting subset of polygons, for instance.

Roads are terribly complicated, so to simplify I tried using Migurski’s High Road. It creates custom views with names like “planet_osm_line_z14” where just roads relevant at that zoom level are present. Also some fancy stuff to make drawing casings vs. road surfaces easier. z15plus is the big set of all roads (170,000); _big is 24000 roads and _small is the other 144,000 lines (footpaths and such). Unfortunately QGIS can’t use the High Road views; details in this issue I filed.

I was able to use the High Road code as a guide for categorizing road by size, though. The “highway” field is the key one. It’s a messy schema, there’s about 7 synonyms for “street”.

Here’s a map of the walks I’ve taken in my neighborhood, with streets and parks.