Cliffs trial and error I think sorry - if you have Photoshop of Elements its method of re-sizing is more in line with what game uses than PaintShopPro's, but depending on percentage you're changing by you still might not end up 'correct'.

You can re-size the larger maps down to act as layer for the smaller maps to try and align things but that isn't 100% accurate.



The sea edges see:
http://www.twcenter.net/forums/showthread.php?t=70584
most of that thread I'm afraid. Basically you need to go manually around map_heights.tga tweaking things. If you scaled up the map_heights originally you'll have everything in 2 pixel jumps when it could be in 1 pixel steps, so you can add detail that way. you can also smooth coast off by having deeper blue sea colours in map_heights as that post explains.