Only some of the sheet effects work with symbols - shadows and glows outside the edge of the symbol, but not much else.

This is easier if you use single tree symbols. Here I have use single trees and put all the symbols onto the same sheet using Change Properties then sorted them all at the same time using Sort Symbols In Map in the Symbols menu.

Thanks guys :)

Remember I'm just one of the crowd though. There are lots of others here working quite hard.

You're probably right. It sounds like a form of transparency acne. Try switching out one of the fills (presumably the grey ones) for a slightly different shade of grey and see if that helps.

Thanks :)

You can if you want, Hadrian, but it's easier to put a whole rectangle of sea over the map and cut holes in it making use of the Color Key effect on the WATER sheet.

It's not really an original idea. Most city map styles have the water over the land. It's just an adaptation of that for overland maps.

30 minute shout :)