Cartographic Skills: Dot Mapping

This week we learned how to create dot distribution maps. Dot maps provide a geographic location of one or more phenomenon. Each dot is geographically placed at its corresponding location and the number of dots changes in proportion to the value for the given geographic location. This provides a view of the overall spatial distribution of data and the density of where the dots exist.

 

We created a dot map for population density in southern Florida. Using Census Bureau data, we portrayed total population statistics for corresponding dots in reference to geographic regions of south Florida. Using Arcmap helped us place dots by using the Symbology tool, we manually created the size of each dot and the density for how many dots we placed on the map. Having dots too large can portray the data inaccurately. Areas might look too dense due to dots being created too large and spanning outside of the dots spatial region. So having smaller dots helps show the actual raw data counts.

When we adjusted the density for the dots, we wanted the dots to just touch each other. If we created more density, we end up with hard to read data as dots start to overlap and cannot be quantified. In Arc we are able to use a slider to manually adjust the density and the dot size, within a preview window, in order to get the right mix of size vs density. 

The great thing about dot maps is we are able to show other layers of data without any loss of visualization for the dots. So we placed a water feature layer on the map. This allowed a view of where water feature are located, which shows why there are no points located within the water features. Without this layer, map readers may question why there are large areas without dots. In Arc we used a masking tool to hide dots that fall within water features. This is any easy option to use but comes at a computer usage cost as masking creates a heavy burden on the speed of the CPU.

With dot mapping, it's useful to show the dots where they are best needed such as urban areas were most of the data exists. Using the masking tool we are able to show dot features that fall within the urban area layer. 

I found this week’s assignment challenging in using the masking tool as it majorly slowed my PC down. It was best to turn off the masking option. So I needed to add and adjust all the map features, before turning on the masking tool. The last option you need to do is turn on the masking tool before you export, making sure everything looks good beforehand was the challenge. I had to go back a few times and redo features and the masking tool slowed me down quite a bit.