Module 4 - Color Concepts and Choropleth Maps

 This weeks lab was a review on the concepts of color use map layouts and the basics of choropleth maps. Naturally, these two topics synched into eachother quite readily as the color scaling we were studying was readily used in the creation of choropleth maps. 

Choropleth maps communicate magnitude through the use of hue values. These magnitudes are usually of  normalized derived data. This means that one does not use choropleth maps to communicate data instances. These maps should be used when relationships between one variable against another variable are being represented, to put it simply. 

One of our tasks was investigating the differneces between linear progression in color ramps and adjusted progressions. What dictates the different values (lightness/darkness) of the hues and their relationship to the original hue is the intervals between the Red, Green, and Blue RGB values. 

In a linear progression, the intervals are equal or close to equal. The simplest way to create this color ramp is to subract the vlaues fo your darkest hues from your lightest and find the average (divide by the remaining amount of desired intervals. 

Below is an example.

For ajdusted progressions, the concept remains the same, however, the first interval is increased by roughly one third and the last decreased by roughly one third. 

One way to easily select or reference color patterns is by using ColorBrewer. Below is an example of one of their progressions. Their inscrease with decesnding intervals of hue and value. 

We were also tasked with creating our own choropleth map and choosing the classifications. We were given the choice of a U.S. state, for this project I selected Colorado. We were given the population data for the years 2010 and 2014 per county. We were tasked with showing the population change and creating a map. 
First off, I used ColorBrewer to select which hue and value ranges I would like to use. Since some counties in Colorado had a negative change and some had a positive, using a divergent color ramp would be the correct choice. I chose a deep blueish green to show the growth in the population and an arid red to show increasing loss of population.
I then used the equal interval classification as this would take the range of counties' percent changes and split that into equal strata to communicate mild to severe population loss. 

6 different classes were used. Since my lowest value was around -14 and my heighest roughly 10.4, I figured I would do three classes above 0 and 3 below. The automatic classification done by ArcGIS Pro unfortunately included nextagtive and positive results in the class that contained the 0 value. To rectify this, I had to manually adjust the class to make the intervals start at 0 for both ascending and descening. 
I then edited the labels of these values to create a simple and effective legend.