The trend towards the liberation of public data, otherwise known as "opendata", means that anyone can access and use certain amount of gegraphic data freely. Those are progressively being released by regional and states gorvernements but also by local communities, and are thus heterogeneous and available in various formats and/or APIs (shp, mif, kml, csv, json, osm, tif...). This conference aims to present general methods to map the territories or 'extents' released onto the web, according to a standardized framework (OGC and W3C standards) which can be duplicated for any type of territory or GIS data (vectors, rasters, tiles...). The various stages of the mapping work will be explained and examplified. Technical details will be given about the Mapserver and Openlayers techniques used for the cartographic rendering. A live demonstration of an application based on such a method and using the Ordance Survey open datasets combined with some OpenStreetMap will also be shown.