+
+## Notes on field values
+
+### place_id is not a persistent id
+
+The `place_id` is created when a Nominatim database gets installed. A
+single place will have a different value on another server or even when
+the same data gets re-imported. It's 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).
+
+Nominatim merges some places (e.g. center node of a city with the boundary
+relation) so `osm_type`+`osm_id`+`class_name` would be more unique.
+
+### boundingbox
+
+Comma separated list of min latitude, max latitude, min longitude, max longitude.
+The whole planet would be `-90,90,-180,180`.
+
+Can we 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 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
+ * 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
+
+They roughly correspond to the classification of the OpenStreetMap data
+according to either the `place` tag or the main key of the object.