1. A map viewer for displaying a three-dimensional, 3d, map view of a 3d geographical map, the map viewer comprising: a database storing data which defines the 3d geographical map, wherein said data comprises at least one of 3d elements, 3d polygons, or wireframes, wherein the database stores the data in a layered hierarchy comprising data layers which can be individually rendered for the 3d map view, wherein the database comprises at least the following data layers: a data layer of a digital terrain model which is modelling a terrain surface, and a data layer of a 3d road network comprising 3d road elements; a processor for rendering the 3d map view and coupled to the database, the processor being configured to: select specific data layers of the database in response to a resolution setting of the 3d map view, wherein the resolution setting of the 3d map view and the selection of the specific data layers of the database are based on a current position of a vehicle in which the map viewer is located, and render the 3d map view using the selected specific data layers of the database; and an optical output device, configured for displaying the rendered 3d map view.