+be found in extra elements as sub-element of `extratags` and `namedetails`
+respectively.
+
+
+## Notes on field values
+
+### place_id is not a persistent id
+
+The `place_id` is an internal identifier that is assigned data is imported
+into a Nominatim database. The same OSM object will have a different value
+on another server. It may even change its ID on the same server when it is
+removed and reimported while updating the database with fresh OSM data.
+It is thus not useful to treat it as permanent for later use.
+
+The combination `osm_type`+`osm_id` is slighly better but remember in
+OpenStreetMap mappers can delete, split, recreate places (and those
+get a new `osm_id`), there is no link between those old and new ids.
+Places can also change their meaning without changing their `osm_id`,
+e.g. when a restaurant is retagged as supermarket. For a more in-depth
+discussion see [Permanent ID](https://wiki.openstreetmap.org/wiki/Permanent_ID).
+
+If you need an ID that is consistent over multiple installations of Nominatim,
+then you should use the combination of `osm_type`+`osm_id`+`class`.
+
+### OSM reference
+
+Nominatim may sometimes return special objects that do not correspond directly
+to an object in OpenStreetMap. These are:
+
+* **Postcodes**. Nominatim returns an postcode point created from all mapped
+ postcodes of the same name. The class and type of these object is `place=postcdode`.
+ No `osm_type` and `osm_id` are included in the result.
+* **Housenumber interpolations**. Nominatim returns a single interpolated
+ housenumber from the interpolation way. The class and type are `place=house`
+ and `osm_type` and `osm_id` correspond to the interpolation way in OSM.
+* **TIGER housenumber.** Nominatim returns a single interpolated housenumber
+ from the TIGER data. The class and type are `place=house`
+ and `osm_type` and `osm_id` correspond to the street mentioned in the result.
+
+Please note that the `osm_type` and `osm_id` returned may be changed in the
+future. You should not expect to only find `node`, `way` and `relation` for
+the type.
+
+### boundingbox
+
+Comma separated list of min latitude, max latitude, min longitude, max longitude.
+The whole planet would be `-90,90,-180,180`.
+
+Can be used to pan and center the map on the result, for example with leafletjs
+mapping library
+`map.fitBounds([[bbox[0],bbox[2]],[bbox[1],bbox[3]]], {padding: [20, 20], maxzoom: 16});`
+
+Bounds crossing the antimeridian have a min latitude -180 and max latitude 180,
+essentially covering the entire planet
+(see [issue 184](https://github.com/openstreetmap/Nominatim/issues/184)).
+
+### addressdetails
+
+Address details in the xml and json formats return a list of names together
+with a designation label. Per default the following labels may appear:
+
+ * continent
+ * country, country_code
+ * region, state, state_district, county, ISO3166-2-lvl<admin_level>
+ * municipality, city, town, village
+ * city_district, district, borough, suburb, subdivision
+ * hamlet, croft, isolated_dwelling
+ * neighbourhood, allotments, quarter
+ * city_block, residental, farm, farmyard, industrial, commercial, retail
+ * road
+ * house_number, house_name
+ * emergency, historic, military, natural, landuse, place, railway,
+ man_made, aerialway, boundary, amenity, aeroway, club, craft, leisure,
+ office, mountain_pass, shop, tourism, bridge, tunnel, waterway
+ * postcode
+
+They roughly correspond to the classification of the OpenStreetMap data
+according to either the `place` tag or the main key of the object.
projects / nominatim.git / blobdiff