Cartography: Module 10 – Dot Density Mapping

     The last couple of weeks have focused on thematic mapping. Dot density mapping is yet another thematic mapping type and was explored in this week’s assignment. Dot density maps are used when the data is conceptual (raw totals) and is not uniformly distributed within the enumeration unit. The dot is then representative of a particular value and placed where that phenomenon is likely to occur. For instance, a dot can represent a given number of individuals (e.g. 1 dot = 10,000) and placed in a populated region (as opposed to an area that is unlikely to be populated).

     These maps are advantageous in that they are easy to interpret and can convey variations in large quantities of data. It is also easy for the user to recreate the original data by simply counting the dots (unless the map is dense or poorly designed). Dot maps take into account ancillary information thus ensuring dot placement in reasonable, logical areas. They are not without issue as there is a human tendency to underestimate density which may affect the map user’s ability to draw the intended conclusion.

    This week’s map is a population density map of South Florida. It was created entirely within ArcMap. The Symbology tab of the Layer Properties contains all of the options for modification of the dot size, value, and color choice. I experimented with combinations of dot size and value until I landed on I choice I felt appropriately represented the data without too many dots converging in densely populated areas. Masking, also found in the Symbology tab (by way of the Properties button once in the Dot Density option), allowed for placement of dots only within urban areas.

A map of the population density of South Florida as depicted through the use of dots.
Each dot represent 25,000. A handful of cities are included to provide reference. 

     My map displays the population density of South Florida with one dot representing 25,000 people. I colored them a bright pink so they would stand out from the other features of the map. Five cities are included to provide a geographic reference. Water features are categorized by type and urban areas are provided for added context. County boundaries are not included to reduce visual clutter and focus the user’s attention on population clusters. I particularly enjoyed this week's assignment as I got to map an area I am familiar with. I am originally from the Miami/Fort Lauderdale area which is chock-full of people (not to age myself, but a while back I went to high school with about 5,000 other students). It is not surprising that the dot map is most dense in this area.