For our deliverable, we used ArcMap to create a dot density map of the population distribution by county throughout South Florida. Dot density mapping is a useful method for showing the geographic distribution of a phenomenon across an enumeration unit, as opposed to a proportional symbol or choropleth map that only shows one value symbol or range throughout the entire unit. You can also use ancillary information, for example, limiting attributes like a lake or relative attributes like urban areas, to create more accuracy in the distribution of the phenomenon by placing dots in, out, or near those attributes. In this case of this map, we used a mask so dots were placed only in urban areas.
One of the disadvantages of dot density mapping, and part of the challenge in this map, is the fact that dot size and value must be adjusted (this case manually) to be big enough to see, of a reader friendly value, showing some density without a jumbled mess, and hopefully show a fairly accurate distribution across the counties. Unfortunately, maybe because of the large area of South Florida, I wasn't able to make the dots large enough to be easily seen and have a reasonably low value without losing some data in the less densely populated counties. A good example of one of the challenges and potentially accuracy issues with dot mapping. The other difficulty that most of us experienced was either ArcMap crashing or very slow rendering speeds once the mask was applied. Not much to do but work around that one. I also debated about leaving or dissolving county boundaries. In the end I decided they were important, as the dot densities were based around census data of counties in South Florida. I did at least get to learn the basics of the dissolve tool with that exploration.
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| Dot density map of the population distribution for counties in South Florida. |
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