Tag with what?
If it's an image you can give it ALT text to descibe in words what the map is showing. In previous versions of Acrobat you could geo-register the map so the measuring tools work in real coordinates, but that is no longer available.
It depends on what you are trying to accomplish. Dave's right about using ALT text to describe the overall map.
What you can do is break your map up into sections the way you'd see a street map, and then give a tag to each of those. In the ALT TEXT for the tag, you could add information like the name of towns or villages in that map segment, roads running through it, ranges of street numbers, and so on. It wouldn't be perfect without a great deal of work, but it would definitely be useful.