External postcode data

Nominatim creates a table of known postcode centroids during import. This table is used for searches of postcodes and for adding postcodes to places where the OSM data does not provide one. These postcode centroids are mainly computed from the OSM data itself. In addition, Nominatim supports reading postcode information from an external CSV file, to supplement the postcodes that are missing in OSM.

To enable external postcode support, simply put one CSV file per country into your project directory and name it <CC>_postcodes.csv. <CC> must be the two-letter country code for which to apply the file. The file may also be gzipped. Then it must be called <CC>_postcodes.csv.gz.

The CSV file must use commas as a delimiter and have a header line. Nominatim expects three columns to be present: postcode, lat and lon. All other columns are ignored. lon and lat must describe the x and y coordinates of the postcode centroids in WGS84.

The postcode files are loaded only when there is data for the given country in your database. For example, if there is a us_postcodes.csv file in your project directory but you import only an excerpt of Italy, then the US postcodes will simply be ignored.

As a rule, the external postcode data should be put into the project directory before starting the initial import. Still, you can add, remove and update the external postcode data at any time. Simply run:

nominatim refresh --postcodes

to make the changes visible in your database. Be aware, however, that the changes only have an immediate effect on searches for postcodes. Postcodes that were added to places are only updated, when they are reindexed. That usually happens only during replication updates.