A beautiful way to finish off an antique-style map is by adding torn edges. There are plenty of free paper textures available online or you could scan some torn paper.
Open the paper texture file, Select All>Copy and paste it onto your document.
Set the blend mode to Multiply and line up the edges so they fit with the edges of your document.
Choose the Eraser tool with a Heavy Scatter Flow tip and set the Opacity to about 60%.
Erase sections of the paper texture and repeat each step until you have a faded, torn effect across the image.