Wikipedia article: Open Location Code
https://plus.codes/map

A proposed system for creating unique IDs for cities (and possibily small territories).

Steps for generating the OLC Code:

1) Look up the city in Wikipedia, which usually gives the geographic center for the location on the page, i.e. Wrocław is given as 51°06′36″N 17°01′57″E.
Wikipedia article: Wroc%C5%82aw

2) Click on the Coordinates link which will take you to GeoHack.
https://geohack.toolforge.org/geoha...

3) From here you can take the Decimal version of the Latitude/Longitude, i.e. 51.11, 17.0325, or click "Google Maps" which will give you a plus code in the left hand information pane https://www.google.com/maps?ll=51.1...

4) Paste that plus code into the search bar:
https://plus.codes/map

5) At the bottom of the OLC map will be the short version of the OLC code, click the up arrow and it will pull-up the left-hand pane which will give the full OLC code, 9F3V426J+2X.
https://plus.codes/9F3V426J+2X

6) Copy the full code to populate the OLC tag.

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Useful for cities that changed names and/or countries over the years:

Before 1721:
Site "Riga, Livonia (Swedish Empire)"
OLC "9G86W4X4+HH"

From 1721 to 1917:
Site "Riga, Livonia (Russian Empire)"
OLC "9G86W4X4+HH"

From 1917 to 1918:
Site "Riga, Livonia (German Empire)"
OLC "9G86W4X4+HH"

From 1918 to 1940:
Site "Riga, LAT"
OLC "9G86W4X4+HH"

From 1940 to 1941:
Site "Riga, LAT (Soviet Union)"
OLC "9G86W4X4+HH"

From 1941 to 1944:
Site "Riga, LAT (Nazi Germany)"
OLC "9G86W4X4+HH"

From 1944 to 1990:
Site "Riga, LAT (Soviet Union)"
OLC "9G86W4X4+HH"

From 1990:
Site "Riga, LAT"
OLC "9G86W4X4+HH"

https://plus.codes/9G86W4X4+HH

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Before 1742:
Site "Vratislav (Austrian Empire)"
OLC "9F3V426J+2X"

From 1742-1871:
Site "Breslau (Prussia)"
OLC "9F3V426J+2X"

From 1871-1945:
Site "Breslau GER"
OLC "9F3V426J+2X"

After 1945:
Site "Wrocław POL"
OLC "9F3V426J+2X"

https://plus.codes/9F3V426J+2X

——————————————————————————————————————————

Site "St. Petersburg RUS"
OLC "9GFGW8P5+XC"

Site "Petrograd RUS"
OLC "9GFGW8P5+XC"

Site "Leningrad RUS"
OLC "9GFGW8P5+XC"

https://plus.codes/9GFGW8P5+XC

——————————————————————————————————————————

From 1824 to 1917:
Site "Kiev RUS (Russian Empire)"
OLC "9G2GCGXF+X8"

1918:
Site "Kiev UKR"
OLC "9G2GCGXF+X8"

From 1919 to 1991:
Site "Kiev UKR (Soviet Union)"
OLC "9G2GCGXF+X8"

After 1991:
Site "Kyiv UKR"
OLC "9G2GCGXF+X8"

https://plus.codes/9G2GCGXF+X8

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Or for uniquely identifing cities with the same name residing in the same country without having to resort to adding an additional territorial identifier to the Site tag (province, district, region, etc.):

Site "Neustadt GER (Rhineland-Palatinate)"
OLC "8FXC9522+22"
https://plus.codes/8FXC9522+22

Site "Neustadt GER (Hesse)"
OLC "9F2FR4X8+XM"
https://plus.codes/9F2FR4X8+XM

Site "Neustadt GER (Brandenburg)"
OLC "9F4JVC8M+M6"
https://plus.codes/9F4JVC8M+M6

Site "Neustadt GER (Bavaria)"
OLC "8FXC84HC+HC"
https://plus.codes/8FXC84HC+HC

Site "Neustadt GER (Schleswig-Holstein)"
OLC "9F6G4R48+V8"
https://plus.codes/9F6G4R48+V8

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And can even be used for countries, territories, and regions when a city isn't given in the source material:

Site "Heligoland"
OLC "9F695VMP+24"
https://plus.codes/9F695VMP+24

Site "Gibraltar"
OLC "8C8P4MR2+22"
https://plus.codes/8C8P4MR2+22

Site "United States of America"
OLC "86G22222+22"
https://plus.codes/86G22222+22

Site "France"
OLC "8FV42222+22"
https://plus.codes/8FV42222+22

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