If you drew the map then theres no easy way to get contours. If you generated the map using a height map first then colored it using some app like Wilbur, Fractal Terrains etc then there is.
Also just a minor point is that if you zoom into a map then the scale is larger. I.e. Large scale mapping is where things are big. We all quote the ratio like 1:50000 or whatever and the 50K number goes up as the world gets smaller but in map terminology its supposed to be a ratio so that its 1/50000 scale so big number = small fraction so 1/72 scale is large scale and 1/1000000 is small. Everyone including me doesn't say it like that tho.
To create a platoon level map yeah just take a small bit and resample that image up big and start mapping on the new image. Take note of the scale tho. You may find that things are supposed to be quite small on it to maintain proper scaling. Check out this months challenge to - heck enter your new map when you do it if its done in time.