A geographer might choose to use a proportional symbol map over a dot density map for several reasons based on the nature of the data being represented:
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Quantitative Representation: A proportional symbol map is particularly effective for representing quantitative data, such as totals or counts, where the size of the symbol (e.g., circles) is directly proportional to the value it represents. This is especially useful for visualizing data that can vary significantly in magnitude.
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Varying Sizes and Intensities: If the subject under study has varying sizes or intensities (e.g., population in different cities), a proportional symbol map can effectively convey this variation by using different sized symbols to represent the magnitude of the data at each location.
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Discrete Units Representation: If the data consists of distinct units (like the number of schools in each city), a proportional symbol map can clearly illustrate the differences in quantitative values among these discrete units. In contrast, a dot density map may not convey the precise quantity as effectively since it emphasizes density rather than exact numbers.
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Consistency Across Locations: When representing data that is more consistent across similar locations but varies gradually over larger distances, a proportional symbol map may provide clearer insights into the overall trend and pattern of the data. In this scenario, the symbol size reflects the magnitude at each point while still allowing for easier interpretation of subtle differences.
In summary, the choice to use a proportional symbol map would likely be influenced by the need to convey quantitative information clearly, show variability, represent discrete units, and illustrate patterns effectively across a geographical area.
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