How to get ALWAYS a city from GPS coordinates?

Question

Hello, I have a GPS coordinates list and I want to retrieve the corrisponding cities.

I'm making calls to Nominatim service, like this: https://nominatim.openstreetmap.org/reverse?format=json&lat=30.4573699&lon=-97.8247654

The response in this case is:

{"place_id":"32590342","licence":"Data © OpenStreetMap contributors, ODbL 1.0. https://osm.org/copyright","osm_type":"node","osm_id":"2785042716","lat":"30.4573699","lon":"-97.8247654","display_name":"Nagoya Steak & Sushi, 11630, RM 620, Anderson Mill, Austin, Williamson County, Texas, 78713, USA","address":{"restaurant":"Nagoya Steak & Sushi","house_number":"11630","road":"RM 620","neighbourhood":"Anderson Mill","city":"Austin","county":"Williamson County","state":"Texas","postcode":"78713","country":"USA","country_code":"us"},"boundingbox":["30.4572699","30.4574699","-97.8248654","-97.8246654"]}

So I can just get the value of city property and obtain the city. What about getting the city when the response doesn't have city property?

According to this answer, I see that I can get other properties, such as town, village, suburb, locality, hamlet and so on... but what is the best? If Nominatim response doesn't have city what property should I look for? And if even that property doesn't appear what should be the next property to try to get the value from?

Can you make a list of these properties, ordered by frequency or relevance?

In addition, what about places that doesn't have any address property? Here is some examples:

http://nominatim.openstreetmap.org/reverse?format=json&lat=19.2954697&lon=-99.1545323 http://nominatim.openstreetmap.org/reverse?format=json&lat=28.7146224&lon=77.1577398 http://nominatim.openstreetmap.org/reverse?format=json&lat=33.2038405&lon=-96.7436876 http://nominatim.openstreetmap.org/reverse?format=json&lat=28.7131567&lon=77.1466021 http://nominatim.openstreetmap.org/reverse?format=json&lat=32.2327348&lon=-81.4502764 http://nominatim.openstreetmap.org/reverse?format=json&lat=35.851869&lon=-79.0196451 http://nominatim.openstreetmap.org/reverse?format=json&lat=19.3709484&lon=-99.1666932 https://nominatim.openstreetmap.org/reverse?format=json&lat=51.6185115&lon=-0.7130883

How to deal with them?

Generally speaking, what is the best strategy to ALWAYS get a city from GPS coordinates?

Accepted Answer

The ALWAYS isn't possible. You might get close, but unless you change the definition of city you have to deal with empty data in your data model.

Not every place (or address) in the world is assigned to a city. People living on small islands will use the name of the island as logical administrative label in their address, it doesn't make it a city.
A city can be multiple types of place. Especially large metropolitan areas are often both city and county, sometimes city and state (Berlin), sometimes city and country (Monaco). OSM data only allows setting one type. In rare cases two places exist in OSM data overlapping each other (same exact boundaries).
OSM data might be missing (explicit) assignments of streets to their city (e.g. with address tagging) or OSM data doesn't contain boundaries of a city. Other than guessing by distance it's unclear where some houses belong to.
Nominatim might not return the city field correctly. When a place exists as node tagged a city, but also relation (same name and/or linked) tagged a village it might return it as village. There's open issues e.g. with London boroughs, Paris Arrondissements and quarters.

https://wiki.openstreetmap.org/wiki/Key:place lists the place types and the right columns of the table have global counts. https://github.com/OpenCageData/address-formatting/blob/master/conf/components.yaml has a hierarchy of fields relevant for an address. https://github.com/openstreetmap/Nominatim/blob/master/lib/ClassTypes.php is Nominatim's internal logic to assign field names.

I would use the components.yaml, look for city aliases and if empty in the Nominatim response move up the hierarchy (county, state...).

How to get ALWAYS a city from GPS coordinates?

Related questions