You could find a picture of an old peice of paper from deviant art to use as the displacement map. Make sure the paper and map are the same size. Image->Adjustments->Desaturate on the paper and save as psd. Go back to the map and Filter->Distort->Displace with 10 for Horizontal Scale and Verticle scale, Stretch to fit and wrap around for the other two settings. Select the paper and your image will distort a little. Then on a new layer on the map, put the paper on a layer above the map and set the paper's layer style to color burn or hard light.