Which map type uses symbol sizes to convey magnitude?

• A. Dot-density map
• B. Choropleth map
• C. Proportional symbol map
• D. Isoline map

Answer: (C)

Using symbol sizes to convey how much of something there is is the hallmark of a proportional symbol map. In this type, each location gets a symbol (often a circle) whose size scales with the data value, so bigger values appear as larger symbols. This makes it easy to compare magnitudes across places at a glance, since the visual cue is the size of the symbol itself. Other types, like dot-density maps (which use a fixed-size dot to represent quantity, with density indicating amount), choropleth maps (which use color shading to represent value), and isoline maps (which use lines of equal value), communicate magnitude through different means, not by changing symbol size.