docs: add new maintenance section

[nominatim.git] / docs / develop / Postcodes.md

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-# Postcodes in Nominatim
-
-The blog post
-[Nominatim and Postcodes](https://www.openstreetmap.org/user/lonvia/diary/43143)
-describes the handling implemented since Nominatim 3.1.
-
-Postcode centroids (aka 'calculated postcodes') are generated by looking at all
-postcodes of a country, grouping them and calculating the geometric centroid.
-There is currently no logic to deal with extreme outliers (typos or other
-mistakes in OSM data). There is also no check if a postcodes adheres to a
-country's format, e.g. if Swiss postcodes are 4 digits.
-
-
-## Regular updating calculated postcodes
-
-The script to rerun the calculation is
-`nominatim refresh --postcodes`
-and runs once per night on nominatim.openstreetmap.org.
-
-
-## Finding places that share a specific postcode
-
-In the Nominatim database run
-
-```sql
-SELECT address->'postcode' as pc,
-       osm_type, osm_id, class, type,
-       st_x(centroid) as lon, st_y(centroid) as lat
-FROM placex
-WHERE country_code='fr'
-  AND upper(trim (both ' ' from address->'postcode')) = '33210';
-```
-
-Alternatively on [Overpass](https://overpass-turbo.eu/) run the following query
-
-```
-[out:json][timeout:250];
-area["name"="France"]->.boundaryarea;
-(
-nwr(area.boundaryarea)["addr:postcode"="33210"];
-);
-out body;
->;
-out skel qt;
-```