I am assuming your map is an image file of some sort; .tif, .jpeg, etc.
You can attach the image in AutoCAD using the IMAGE command. That way, the map remains in the background in AutoCAD and no entities are added to your file, thus keeping your file size manageable.
You can then push the image behind any AutoCAD entities you would like to draw on top of the map.
If you need to have the physicals entities of the map inside your file, then you could look at getting a raster to vector program to convert the map.
