The Vale LARP game is played at Huntley Wood, which is essentially 170 acres of former quarry. Scattered across the quarry are a half a dozen resource spawn points. The idea is to camp on these points and collect the resources as they spawn, while avoiding the opposing side who are trying to do the same. I figured that an exploration map like this would be extremely useful.
The base plate has a map of the site engraved upon it, a raised lip all around the edge turns this into a sand tray. With a bit of sprinkling and shaking you can cover up the entire map leaving only the starting location exposed. As people explore round the site they can brush the sand away exposing the map. This way everybody knows the areas that haven't been searched for resource nodes. Once the nodes are discovered tokens are added to the map to show exactly where they are.
This map was pretty useful for our teams success at the weekend just gone. People were also using it to discuss ambushes and attack plans once the sand was cleared off 90% of the board. It also explains why I didn't want to show it to you guys until after the event, don't want those sneaky Dukes people stealing my ideas.