# OSM Data Import
-OSM data is initially imported using osm2pgsql. Nominatim uses its own data
-output style 'gazetteer', which differs from the output style created for
-map rendering.
+OSM data is initially imported using [osm2pgsql](https://osm2pgsql.org).
+Nominatim uses its own data output style 'gazetteer', which differs from the
+output style created for map rendering.
## Database Layout
motorway bridge. In OSM, this would be a way which is tagged with
`highway=motorway` and `bridge=yes`. This way would appear in the `place` table
once with `class` of `highway` and once with a `class` of `bridge`. Thus the
-*uique key* for `place` is (`osm_type`, `osm_id`, `class`).
-
-## Configuring the Import
-
-How tags are interpreted and assigned to the different `place` columns can be
-configured via the import style configuration file (`CONST_Import_style`). This
-is a JSON file which contains a list of rules which are matched against every
-tag of every object and then assign the tag its specific role.
-
-### Configuration Rules
-
-A single rule looks like this:
-
-```json
-{
- "keys" : ["key1", "key2", ...],
- "values" : {
- "value1" : "prop",
- "value2" : "prop1,prop2"
- }
-}
-```
-
-A rule first defines a list of keys to apply the rule to. This is always a list
-of strings. The string may have four forms. An empty string matches against
-any key. A string that ends in an asterisk `*` is a prefix match and accordingly
-matches against any key that starts with the given string (minus the `*`). A
-suffix match can be defined similarly with a string that starts with a `*`. Any
-other string constitutes an exact match.
-
-The second part of the rules defines a list of values and the properties that
-apply to a successful match. Value strings may be either empty, which again
-means that thy match against any value, or describe an exact match. Prefix
-or suffix matching of values is not possible.
-
-For a rule to match, it has to find a valid combination of keys and values. The
-resulting property is that of the matched values.
-
-The rules in a configuration file are processed sequentially and the first
-match for each tag wins.
-
-A rule where key and value are the empty string is special. This defines the
-fallback when none of the rules matches. The fallback is always used as a last
-resort when nothing else matches, no matter where the rule appears in the file.
-Defining multiple fallback rules is not allowed. What happens in this case,
-is undefined.
-
-### Tag Properties
-
-One or more of the following properties may be given for each tag:
-
-* `main`
-
- A principal tag. A new row will be added for the object with key and value
- as `class` and `type`.
-
-* `with_name`
-
- When the tag is a principal tag (`main` property set): only really add a new
- row, if there is any name tag found (a reference tag is not sufficient, see
- below).
-
-* `with_name_key`
-
- When the tag is a principal tag (`main` property set): only really add a new
- row, if there is also a name tag that matches the key of the principal tag.
- For example, if the main tag is `bridge=yes`, then it will only be added as
- an extra row, if there is a tag `bridge:name[:XXX]` for the same object.
- If this property is set, all other names that are not domain-specific are
- ignored.
-
-* `fallback`
-
- When the tag is a principal tag (`main` property set): only really add a new
- row, when no other principal tags for this object have been found. Only one
- fallback tag can win for an object.
-
-* `operator`
-
- When the tag is a principal tag (`main` property set): also include the
- `operator` tag in the list of names. This is a special construct for an
- out-dated tagging practise in OSM. Fuel stations and chain restaurants
- in particular used to have the name of the chain tagged as `operator`.
- These days the chain can be more commonly found in the `brand` tag but
- there is still enough old data around to warrant this special case.
-
-* `name`
-
- Add tag to the list of names.
-
-* `ref`
-
- Add tag to the list of names as a reference. At the moment this only means
- that the object is not considered to be named for `with_name`.
-
-* `address`
-
- At tag to the list of address tags. If the tag starts with `addr:` or
- `is_in:`, then this prefix is cut off before adding it to the list.
-
-* `postcode`
-
- At the value as a postcode to the address tags. If multiple tags are
- candidate for postcodes, one wins out and the others are dropped.
-
-* `country`
-
- At the value as a country code to the address tags. The value must be a
- two letter country code, otherwise it is ignored. If there are multiple
- tags that match, then one wins out and the others are dropped.
-
-* `house`
-
- If no principle tags can be found for the object, still add the object with
- `class`=`place` and `type`=`house`. Use this for address nodes that have no
- other function.
-
-* `interpolation`
-
- Add this object as an address interpolation (appears as `class`=`place` and
- `type`=`houses` in the database).
-
-* `extra`
-
- Add tag to the list of extra tags.
-
-* `skip`
-
- Skip the tag completely. Useful when a custom default fallback is defined
- or to define exceptions to rules.
-
-A rule can define as many of these properties for one match as it likes. For
-example, if the property is `"main,extra"` then the tag will open a new row
-but also have the tag appear in the list of extra tags.
-
-There are a number of pre-defined styles in the `settings/` directory. It is
-advisable to start from one of these styles when defining your own.
-
-### Changing the Style of Existing Databases
-
-There is normally no issue changing the style of a database that is already
-imported and now kept up-to-date with change files. Just be aware that any
-change in the style applies to updates only. If you want to change the data
-that is already in the database, then a reimport is necessary.
+*unique key* for `place` is (`osm_type`, `osm_id`, `class`).
projects / nominatim.git / blobdiff