A
Geocode (
Geospatial
Entity
Object
Code) is
code that represents a geospatial coordinate measurement of an exact
geographic location and time at, below, or above the surface of the earth.
A Geocode representation is derived from the following geospatial attributes: 1. Latitude 2. Longitude 3. Altitude 4. Date 5. Local Time 6. Global Time 7. Other geospatial attributes such as:
A Geocode is an all-natural number representation.
how the area is coded (number, letter, mixture of both, other)
which part of the earth is covered (whole earth, land, water, a continent, a country)
what kind of area or location is coded (country, county, airport, railstation, city)
whether an area or a point is coded

List of some code systems Some of these code systems are free for use, others have different
licences.
Car
License plates C-squares - compact encoding of geographic coordinate bounds (latitude-longitude)
FIPS country codes (FIPS 10-4), area code, administrative, free
FIPS place codes (FIPS 55)
U.S. only, free
FIPS county codes (FIPS 6-4) US only, free
FIPS state codes (FIPS 5-2) US only, free
Georef, a military / air naviation co-ordinate system for point and area identification
IATA airport codes, area /point codes, airports
ICAO airport codes, area /point codes, airports
IANA country codes similar to
ISO 3166-1 alpha-2 IOC country codes, area, worldwide
ISO 3166 country and subdivision codes
ITU-R country codes ITU-T country calling codes ITU-T mobile calling codes Maidenhead Locator System MapDot Protocol: world locations coded into a zone sequence
[1], free
MARC country codes Marsden Squares NAC, area codes (area can be indefinitely small)
NUTS area code, partially administrative, worldwide: countries, Europe : country to community
ONS code,
UK only, administrative
Postal codes, area, worldwide, country-codes by
UPU, free
Quarter Degree Grid Cells UN M.49 region codes, area code, continents, countries (like
ISO 3166-1 numeric)
SALB (Second Administrative Level Boundaries), by UN
[2] UN/LOCODE, area, administrative, cities
UTM WMO squares