Correct Answer:
C. on
The correct answer is on. The preposition 'on' is used to indicate that something is located on a surface, such as a map, a page, or a wall. When you look for a town, you expect to find its representation 'on' the surface of the map.
- at: 'At the map' would imply being physically present at the location of the map, not finding something depicted within it.
- with: 'With the map' suggests accompaniment or using the map as a tool, not a location on its surface.
- over: 'Over the map' implies being positioned above the map, not being a part of its content.