GeoNames Forum

I have some questions about the methodology for obtaining postal code mappings on geonames.

How is the mapping from postal codes to latitude/longitude coordinates derived? Are postal codes first mapped to cities and then assigned the coordinates of the corresponding cities? Or are postal codes mapped to coordinates that are specific to the postal codes?

Also, for which countries does geonames have official or high precision postal code to city and postal code to latitude/longitude data? For which countries are these mappings derived from postal code - city name co-occurrences in search results?

Thanks!

It is not one way or the other, it depends on the data available for a postal code. The column 'accuracy' gives an indication of how accurate the lat/lng for a postal code is.
For lack of other data in most cases it derived from the lat/lng of the corresponding city.

postal code - city name co-occurence is only used to determine the sort order. Combinations that have more hits on searches rank higher than combinations with lesser hits.

Marc