Hi, I've written a little analysis of the Zoom-Selector and possible interpretations:
http://wiki.openstreetmap.org/wiki/User:Bk/MapCSS#Zoom Basically, when you have a TMS (like the Openlayers map on openstreetmap.org), the tiles at a given zoom level don't have the same scale. In fact it varies quite a lot: E.g. zoom 18 tiles at the equator have scale of 1.7 px per meter, but at 60° latitude they have a scale of 3.3 px per meter. (The distortion comes from the Mercator projection) This means, if a renderer ties the MapCSS zoom levels to TMS tile-levels, a typical city map of 5 km x 5 km may be rendered very differently depending on the location of the city on the earth. For these reasons, the zoom levels in the Mapnik style file do *not* map exactly to tile levels, but are converted to scales first. In my opinion, it should be the same in MapCSS and the definition of the zoom selector should be based on map scale rather than on the projected coordinates in the Mercator projection. Paul _______________________________________________ Mapcss mailing list [email protected] http://lists.openstreetmap.org/listinfo/mapcss
