Answer:
3) to determine the best location for a new road
Step-by-step explanation:
Since the question indicates the person using the topography map is an engineer, we have to assume it's for a use related to work... otherwise the question would have said "someone".
1) to find an area used for camping
That's a valid use for a topography map, but not a work-related one.
2) to define a political boundary line
That's also a valid use of a topography map, but it wouldn't be used for that by an engineer, more like a politician since it would be about political border.
3) to determine the best location for a new road
YES. That's a valid use and it's a professional use related to an engineer, a civil engineer in this case.
4) to find the ideal place to hike on a mountain
Another valid use, but not specific to work.
Turns out, all four possible answers are valid uses of a topography map, but only one related to engineer work.