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Pgsql Backend

The pgsql backend is designed for rendering OpenStreetMap data, principally with Mapnik, but is also useful for analysis and exporting to other formats.

Database Layout

It connects to a PostgreSQL database and stores the data in four tables:

  • planet_osm_point
  • planet_osm_line
  • planet_osm_roads
  • planet_osm_polygon

planet_osm_roads contains the data from other tables, but has tags selected for low-zoom rendering. It does not only contain roads!

The default prefix planet_osm can be changed with the --prefix option.

If you are using --slim mode, it will create the following additional three tables which are used by the pgsql middle layer, not the backend:

  • planet_osm_nodes
  • planet_osm_ways
  • planet_osm_rels

With the --flat-nodes option, the planet_osm_nodes information is instead stored in a binary file.

Note: The names and structure of these additional tables, colloquially referred to as "slim tables", are an internal implemention detail of osm2pgsql. While they do not usually change between releases of osm2pgsql, be advised that if you rely on the content or layout of these tables in your application, it is your responsibility to check whether your assumptions are still true in a newer version of osm2pgsql before updating. See osm2pgsql-dev#230 for a discussion of the topic.

Importing

  1. Runs a parser on the input file and processes the nodes, ways and relations.

  2. If a node has a tag declared in the style file then it is added to planet_osm_point. Regardless of tags, its position is stored by the middle layer.

  3. If there are tags on a way in the style file as linear but without polygon tags, they are written into the lines and, depending on tags, roads tables.

    They are also stored by the middle layer.

  4. Ways without tags or with polygon tags are stored as "pending" in the middle layer.

  5. Relations are parsed. In this stage, multipolygon and boundary relations are turned into polygons. Route relations are turned into linestrings.

  6. "Pending" ways are processed, and they are either added as just the way, or if a member of a multipolygon relation, they are processed as multipolygons.

  7. Indexes are built. This may take substantial time, particularly for the middle layer indexes created in non-slim mode.