Map Markup Language is hypertext for Web maps, like HTML is hypertext for Web pages. See the explainer document.
Maps on the Web have evolved significantly over the years. Yet in all that time, maps and the mapping community have not become significant contributors to the Web standards community. There are many reasons for this, but it is possible that one major cause is due to the lack of a common Web format for maps.
MapML aims to be a simple format which strictly relies on existing Web standards and best practices with special emphasis on URLs and simple hypertext for state transitions, and standard styling techniques. The objective is to enable the convergence of modern Web mapping into the main stream of Web standards, to the mutual benefit of both the web and mapping communities.
MapML is being developed by the W3C Maps for HTML Community Group. Membership in that group is encouraged, however you do not have to join to use the information found here. However, if you wish to contribute, please join the Maps for HTML Community Group, and help us make the Web a map-friendly platform for everyone, everywhere!