Wikipedia:GEOUF

Geo is a microformat used for marking up WGS84 geographical coordinates (latitude;longitude) in (X)HTML. Although termed a "draft" specification, this is a formality, and the format is stable and in widespread use; not least as a sub-set of the published hCalendar and hCard microformat specifications, neither of which is still a draft.

Use of Geo allows parsing tools (for example other websites, or Firefox's Operator extension) to extract the locations, and display them using some other website or mapping tool, or to load them into a GPS device, index or aggregate them, or convert them into an alternative format.

The Geo microformat is applied using three HTML classes. For example, the marked-up text:

<div>Belvide: 52.686; -2.193</div>

becomes:

<div class="geo">Belvide: <span class="latitude">52.686</span>; <span class="longitude">-2.193</span></div>

by adding the class-attribute values "geo", "latitude" and "longitude".

This will display

Belvide: 52.686; -2.193

and a geo microformat for that location, Belvide Reservoir, which will be detected, on this page, by microformat parsing tools.

Each Geo microformat may be wrapped in an hCard microformat, allowing for the inclusion of personal, organisational or venue names, postal addresses, telephone contacts, URLs, pictures, etc.

There are three active proposals, none mutually-exclusive, to extend the geo microformat:

Organisations and websites using Geo include:

Many of the organisations publishing hCard include a geo as part of that.

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Wikipedia