Lab 6: Proportional Symbol and Bivariate Choropleth Mapping

 

When an attribute table has negative values they must be converted to positive before mapping. First you must separate the values to be mapped, in this case, jobs lost and gained. Make a selection of the values needed to create another feature, then use simple math of multiplying a negative by -1 to keep the same values. Then you have two different features to be mapped, positive and negative but it is easy to work. Proportioned dots stacked on each other with different sizes are effective. (The purple background in this map is the result of fatigue and is terrible.)

I used the ColorBrewer website to pick a 3-color classification. Once selected then the information was displayed for me. I chose three 3 color classifications with similarities in tones, which allowed to keep hues that complemented each other. In ArcGIS I opened each color of the symbology to ensure I had the matching numbers when applying the color scheme to each value.

H 321 S 86 V 77	H 277 S 48 V 65	H332 S 87 V 86
H 345 S 36 V 98	H 210 S 27 V 85	H 302 S 26 V 78
H 6 S 12 V 99	H 204 S 8 V 95	H 266 S 5 V 26

Bivariate choropleth mapping is great because of its efficiency in providing information. Having two variables that are related drives home the point better because of the link. In the lab, obesity and physical inactivity are two very good examples of complementary variables. Typically, one does not go without the other, although that is not always the case. In creating this type of map, it can also help bring an understanding that there may be an issue of concern is being addressed and shows a trend in specific areas. For obesity and physical inactivity, it may seem common knowledge they go together but creating a legible, balanced, and good visually contrasted map really can be a powerful tool of information.