Concept:The division of settlements into rural and urban is based mainly on population size and density.
Explanation:To rank settlements, authorities commonly use population counts.
Urban settlements generally have large and dense populations, while rural settlements have smaller and less dense populations.
Location only tells where a settlement is situated, not its ranking.
Pattern describes the layout or shape of the settlement, which is unrelated to rural-urban grouping.
Even the physical area or size of a settlement may differ without changing its classification.
Therefore, the most common basis for ranking is population.
Answer:D. population