So I finally sorted out the problem I've been working on for a few days.

Now when you select a unit it highlights all tiles that are within a set distance of the unit (currently hardcoded to 3). I'll add in a cost based on the tile type over the next few days. Also need to make the highlight list remove duplicates as you may notice some of the tiles are double highlighted in the screenshot.

I had given up on this earlier today after several hours but had another quick look at it for 10 mins and had one of those great "oh yeah!" moments and fixed it. Programming can be massively frustrating at times :p