Turn on Map filters -> Neighbours. Shows every connection of selected province.
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I also have a confession of sorts. I spent ages redrawing the borders on this map a while ago. I didn't want to influence the map choice and I wanted to test it in game so I've kept schtum till now.
It has antialased and more accurate borders and two versions with varying brightness. Connections between caves are drawn in (some surprises there too no doubt):
http://forum.shrapnelgames.com//showthread.php?t=47976
IMPORTANT: the images are fully interchangeable but don't swap the map script (as jimbo customised ours). Just put one of the new images in place of the old one and reload dom3 (must quit to desktop) to try the other map pic. Everything will be the same but the background.