If your planning to get it printed then yes. If your using it on the screen or in a virtual table top then you could go lower. Also if your map is like 5ft x 4ft then thats a big map at 300 ppi so maybe just go lower anyway. But usually and if able, 300 pixels per inch is a good idea. So an A4 image is about 3500x2500 or thereabouts. You can create the image with a setting for 300 dpi / ppi and then set the inches directly.