This guide explains how data sources other than OpenStreetMap mentioned in
the install instructions got obtained and converted.
+
+## Country grid
+
+Nominatim uses pre-generated country borders data. In case one imports only
+a subset of a country. And to assign each place a partition. Nominatim
+database tables are split into partitions for performance.
+
+More details in [osm-search/country-grid-data](https://github.com/osm-search/country-grid-data).
+
+## US Census TIGER
+
+For the United States you can choose to import additonal street-level data.
+The data isn't mixed into OSM data but queried as fallback when no OSM
+result can be found.
+
+More details in [osm-search/TIGER-data](https://github.com/osm-search/TIGER-data).
+
+## GB postcodes
+
+For Great Britain you can choose to import Royalmail postcode centroids.
+
+More details in [osm-search/gb-postcode-data](https://github.com/osm-search/gb-postcode-data).
+
+
+## Wikipedia & Wikidata rankings
+
+Nominatim can import "importance" data of place names. This greatly
+improves ranking of results.
+
+More details in [osm-search/wikipedia-wikidata](https://github.com/osm-search/wikipedia-wikidata).
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