How to get areas/regions for a country and cities for this area/region? - geolocation

Question

We made a simple query which gets some cities:
SELECT * FROM `allCountries` WHERE name='Moscow' and `country_code` = 'RU'
Here is the result of this query:
For example, for another city we get a result with 4-7 rows.
How to get all areas/regions for a country and then get all cities for this area/region?
P.S.: Please be careful. We are not interested in an API site and database fetch. Thanks!

Answer 1

Background
In Geonames you have feature_classes and feature_codes which discriminate the location type. You can find detailed description of the code in the Geonames website. As in your snapshot, P.PPLC means "City (populated place) which is capital of a political entity" and S.HLC means "building (spot) hotel".
Also, every geoname have properties to identify the location in the "hierarchy" inside a country; this properties are country_code, admin1_code, admin2_code, admin3_code, admin4_code. Note that not all properties are used for every given geoname, since this depends on the political organization of a country.
Find all city inside an administrative level
To find all city inside an area (i.e. administrative level), you must first search the geoname for that admin level, in order to have the admin codes useful to filter the city query.
To find an admin level, you must first execute a query like:
SELECT *
FROM `allCountries`
WHERE `country_code` = 'RU'
AND `feature_class`='A'
AND `feature_code`='ADM1'
Note that the query filter out only the first admin levels (feature_code='ADM1'), but you can find admin level of any depth by changing it to:
SELECT *
FROM `geonames`
WHERE `country_code` = 'RU'
AND `feature_class`='A'
AND `feature_code` LIKE 'ADM_'
Now, select one record from this result set and you it to search for the cities, by using the "hierarchy" codes of that level. You should use something like (mutatis mutandis):
SELECT *
FROM `geonames`
WHERE `country_code` = "RU"
AND `feature_class`='P'
AND `feature_code` LIKE 'PPL%'
AND `admin1_code`="<admin1>"
AND `admin2_code`="<admin2>"
AND `admin3_code`="<admin3>"
AND `admin4_code`="<admin4>"
Beware of NULL admin codes, which you need to strip out from the SQL (the whole "AND ..." clause).
Of course, you can do the original "Moscow" search inside this filtered set.

Answer 2

The answer for your question is pretty long, but this code snippet may help you a little bit. These queries obtain all hierarchy information about given geonameid (it's plpython inside postgres).
get_geoname = plpy.prepare("SELECT geonameid, asciiname, country, admin1, admin2 FROM all_countries where geonameid=$1",
["integer"])
get_country_name = plpy.prepare("SELECT name as country from country_info where code = upper($1)", ["varchar"])
get_admin1 = plpy.prepare("SELECT asciiname, name FROM admin1 where code = $1", ["text"])
get_admin2 = plpy.prepare("SELECT asciiname, name FROM admin2 where code = $1", ["text"])