I've noticed on the geonames Postal Codes search for USA that searching for a town that does not exist in Postal Code table (like North Avon) brings up the zipcode for that place, even thought there is no direct link between the two table. I thought it was lat/long comparison but the search seems too fast for that. Can anyone please guide me on this how two tables are linked?
The two tables are not (yet) linked for the US. The result you get for 'North Avon' are in fact the results for 'Avon'. The search term 'north' is also found in the continent name 'North America'. So you get all places in 'North America' with the name 'Avon'.