My map pics went down a couple of years ago when the hosting site crashed (ISP did an unannounced OS upgrade ... ::) ). And it helps I've been here since before dirt ;)
Anyway, I resurrected a few shots.
They're exactly map scale, so I could (if I wanted) use them with standard maps.
Process was labourious, but simple.
1) Got standard 1" thick foam sheets from hardware store.
2) Base map sheets got trimmed to size.
3) I took an A4 sheet of clear plastic, and laid it on a BT map. I then marked the hex joints with a dot of permanent marker. Later, I drilled out the dots
4) Lay the overlay on the sheet, and use a whiteboard marker to dab on each hole. This leaves you with a pattern of hexagons marked out in dots. Move the sheet, be careful to keep alignment, then repeat until sheet is covered.
5) I then used a cunning home-made tool (Worktroll's Wheel) to manually push the hex-lines into the sheet.
6) For elevations, I then marked & cut out the required shapes, using one of those extensible, snap-off craft knives. (Yes, a hot wire cutter would have been easier, but I didn't have one. Pro tip - every couple of minutes, cut the knife into a wax candle. This keeps the edge from sticking on the foam beads.). They were then glued into place.
6) A coat of leftover green housepaint, and some pipe-cleaner trees on the hex points, and voila!
I did up 9 of these, all standard BT maps. In retirement, I may resume and do the moonscape, and canyon maps. But as I haven't played for so long at the moment, they're mainly photo backdrops :(