GIS 3015 Lab 11: Dot Density Mapping

This week's lab introduced us to the relatively specialized dot density map.  This style of thematic map represents data in the form of dots distributed across the map surface.  In the example above, I created a population map of southern Florida wherein each dot equals 20,000 people.  Dot density maps have the advantage of being simple and intuitive to read for the basic information communicated.  However, the distribution of the dots may also intuitively suggest to the observer the actual data distribution when in fact the dots are placed randomly.  To ameliorate this weakness, we can choose to include and exclude different areas on the map that dots may be drawn based on other data layers.  Thus, based upon what we know about the data, we can more accurately portray where the data should best be located.  In the example above, the dots representing population were excluded from the surface water layer and further limited to a layer representing urban areas (not symbolized).  While the dots were still drawn randomly given those limitations, we can be safe in assuming the resulting dot placement is more accurate than without such criteria.

Many of us ran into issues with ArcMap as we worked through the process of finalizing our maps.  We learned, for instance, that drawing the dots for the dot density map is an immense strain on the software. This is compounded when making other edits with the layout, creating delays each time.  To minimize this issue, the lab instructions had us turn off masking (i.e., the inclusion and exclusion criteria).  Combined with the fixed placement option, this would theoretically allow us to create our layouts with fewer software delays.  However, when turned back on, the dot placement did not recognize the inclusion and exclusion placement criteria.  I experimented with different orderings of the data layers in the table of contents with no effect.  For my second attempt, I created a fresh map and, rather than turning off masking, I simply unchecked the south Florida layer so it did not display.  This method worked and allowed me to complete the above map.