A choropleth map (from Greek χῶρος "area/region" and πλῆθος "multitude") is a type of thematic map in which areas are shaded or patterned in proportion to a statistical variable that represents an aggregate summary of a geographic characteristic within each area, such as population density or per-capita income.
Although opportunity cost is definitely important, it is hard to put a "price" on the opportunity in many cases, which makes it unmeasurable. This is why economists focus almost exclusively on price.
