Imagine drawing a simple map of your sand table. On it, you indicate where certain small toys can be found (you have buried them there, previously). Children (I would suggest one at a time) can go over to the table and using the map unearth the hidden objects. Of course, children can simply dig around and find the objects, but if you design this activity specifically for the purpose of map use, the children will know that this is a game with a specific set of rules to follow.
You may have to help children under 4 orient the map so they can mentally imagine how the map lines up to the actual sand table. This mental rotation of objects in space is a fundamental geometric skill.
This activity can be repeated using simple maps of areas all over your center, classroom, and outdoor spaces. It works just like hide and seek except there is map, clues, and investigation involved. If you create some good ones, go ahead and get them laminated and then they can be used and reused over and over again, with dry erase markers.