If a state has low overall density but very high density in a river valley, which study will be more useful?

Correct answer: Micro-regional density study

Direct answer: Option C, a micro-regional density study. Population density is the number of people living in a unit of area, usually one square kilometre. A state average combines cities, river valleys, forests, hills and sparsely settled areas into one figure. Consequently, a low average does not mean that every part of the state is thinly populated. A smaller regional study can map the valley separately and compare it with surrounding areas. The valley may support farming, settlements, transport and economic activity, so its local density can be much higher. Option A is insufficient because memorising the average hides local variation. Option B removes the very measure needed for comparison. Option D is wrong because the river valley is central to understanding the settlement pattern, even though the river alone does not explain every detail. Memory cue: an average is a summary, not a map of every place.