Eurowiki:WikiProject Geographical coordinates/source:

Specifies, where present, the data source and data source format/datum, and optionally the original data, presented in parentheses. This is initially primarily intended for use by geotagging robots, so that data is not blindly repeatedly copied from format to format and Wikipedia to Wikipedia, with progressive loss of precision and attributability.

Examples:
 * A lat/long geotag derived from an Ordnance Survey National Grid Reference NM 435 355 found in the English-language Wikipedia would be tagged as "source:enwiki-osgb36(NM435355)"
 * A latitude-longitude location sourced from data taken from the German-language Wikipedia would be tagged as "source:dewiki" – and so on, for other language codes;
 * A location sourced from the public domain GeoNet Names Server database would be tagged as "source:GNS". No datum or format information is needed, since by default all Wikipedia coordinates are in latitude/longitude format based on the WGS84 datum. Similarly, US locations sourced from the similar public domain GNIS database would be tagged as "source:GNIS".