GIS 6005 Module 4 Color Concepts & Choropleth Mapping

 The first part of this lab focused on color concepts. We explored the relationship between RGB and HSV color systems and compared the color ramps on ArcGIS Pro with those on ColorBrewer. We were asked to create three different color ramps to explore the differences and better understand the processes used to create them. We selected a color, then created a linear progression ramp, an adjusted progression ramp, and lastly, selected the closest match to the previous ramps on ColorBrewer. Below is a screenshot of each of the ramps, interval information, and notes.

The differences between my linear progression and my adjusted progression color ramps are subtle. The greatest difference being the increased step size between the darkest colors in the adjusted progression ramp which I used to help the map viewer (person) differentiate them. The Color Brewer ramp number were very different than either of my color ramps. The results generated a progression of colors that I felt more defined and easier to distinguish from each other. The RGB values show that Color Brewer varied the steps between each color selection much more than my linear progression or my adjusted progression ramps. The results reflected our text/readings and illustrated just how complicated the relationship is between RGB values when creating color ramps. This lab also showed how difficult choosing the best color ramp can be and how time-consuming custom creation is.

Choropleth Map

The final map we made was one to show the changes in population by county for the state of Colorado from 2010 to 2014.

For a coordinate system, I selected NAD 1983 (CORS96) State Plane Colorado Central FIPS 0502 (US Feet). The State plane coordinate systems are designed specifically for individual states or regions. They minimize distortion within that specific area, making them ideal for these maps where accuracy is important. Colorado Central is one of the three zones within the Colorado State Plane system, optimized for the central part of the state. As this map covers the entire state, I felt it was the best choice. I selected feet instead of meters because the average American is more familiar with feet than meters.

To normalize my data I used Arcade for my formula ((POP2014 – POP2010)/POP2010)*100. This calculation resulted in both positive and negative values. I elected to use a diverging color ramp, along with an odd number of classes (seven), which I felt was best for visualizing the divergent changes in population. For classification, I used a Natural Breaks (Jenks) because this method best depicted the relationship in range of values, as opposed to using the total county counts per class. 

On the map layout I elected to go with the symmetrical classification around zero. I felt communicated the most amount of information to the average view at a glance. I started with five classes but felt that was not sufficient and that seven gave a better picture of the divisions.