After quite a long time, I have rediscovered GeoURL. This is a sevice that allows to find web sites that are near a given geographic location.
After redesign of the web, which now also includes a blog, a Firefox extension has been created for looking up which sites are near the web page you are visiting.
In order to notify this web site and all the visitors, a meta tag must be added in the header of your site.

<meta ICBM='xxxxx, yyyyy'>

where xxxxx is the longitude and yyyyy is the latitude.

GeoURL and the very extension also analyze Geo tags, that were originally proposed from an equivalent service named Geo Tag.

All these tags do not appear standard. However, since they are meta tags, it does not entail any problem for browsing.

There is a standardization initiative of meta tags for multiple purposes named Dublin Core Metada Initiative.