the map is, well, the map... It is found here: http://map.aypok.co.uk/index.php
to use it, click on the suburb name that you want to see (your current suburb is found at the top of the view on the game screen) and it will show a complete map of the area. You may want to look up a suburb on the wiki as well, as it gives danger levels and (potentially) barricade plans. It also shows co-ordinates that are viewable in game with a gps http://wiki.urbandead.com/index.php/GPS#GPS_Unit
the toolbar is a useful (purely optional) utility that contains useful links and enhances the graphics slightly, only works in firefox, found here: http://udtoolbar.mozdev.org/
