The idea is simple; you choose a photograph that shows a town, valley, mountain range, castle, etc. You map the area around it. This is not a challenge to map the structure itself, but rather to include the elements of the whole photograph, esp the background, into the map you make. For example, this image of Marksberg Castle in Germany shows some of the terrain. You would want to create a map that has the river, hills, etc around the castle - but it doesn't have to be a local map.