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28 lines
1.3 KiB
Markdown
28 lines
1.3 KiB
Markdown
# OSM Data Import
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OSM data is initially imported using [osm2pgsql](https://osm2pgsql.org).
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Nominatim uses its own data output style 'gazetteer', which differs from the
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output style created for map rendering.
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## Database Layout
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The gazetteer style produces a single table `place` with the following rows:
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* `osm_type` - kind of OSM object (**N** - node, **W** - way, **R** - relation)
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* `osm_id` - original OSM ID
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* `class` - key of principal tag defining the object type
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* `type` - value of principal tag defining the object type
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* `name` - collection of tags that contain a name or reference
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* `admin_level` - numerical value of the tagged administrative level
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* `address` - collection of tags defining the address of an object
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* `extratags` - collection of additional interesting tags that are not
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directly relevant for searching
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* `geometry` - geometry of the object (in WGS84)
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A single OSM object may appear multiple times in this table when it is tagged
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with multiple tags that may constitute a principal tag. Take for example a
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motorway bridge. In OSM, this would be a way which is tagged with
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`highway=motorway` and `bridge=yes`. This way would appear in the `place` table
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once with `class` of `highway` and once with a `class` of `bridge`. Thus the
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*unique key* for `place` is (`osm_type`, `osm_id`, `class`).
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