KML (Keyhole Markup Language) is an XML-based file format for describing geographic objects, used in particular by Google Earth and Google Maps.
Heurist has some support for importing KML files - this is currently the only practical method for adding large amounts of geographic data to the system.
KML is natively exported by Google Earth. Other applications can export data in KML format using a plugin, including ArcGIS and CartoWeb. The format of KML is documented online so it is possible to "hand roll" your own KML by hand, using an XML editor.