Cartography - Module 6 -- Data Classification

     There are various was to classify and display data on your map. This week the lab assignment focused on methods of data classification. In particular, it reviewed natural breaks, equal interval, quantile, and standard deviation methods. The result is a map displaying these four classification methods for a given dataset. I will briefly discuss each classification method and then my map.
     Without going into too much detail, each method has their advantages and disadvantages. They define their classes differently and thus display data differently. The equal interval method generates classes that have equal ranges while the quantiles method divides the data into classes with equal numbers of observations. Thus, for quantiles, the classes have different ranges. Likewise, the natural breaks method has class ranges that differ. This method uses algorithms to minimize within class variance but maximize between class variance. The final method, standard deviation, performs exactly as it is named. It separates the data into classes based upon their deviation from the mean.
     The exercise was performed in ArcMap using their classification tools within the layer properties menu. Default settings for all methods were used. Standard deviation classification uses a default seven classes while the remaining methods use five classes.

A map displaying a dataset classified using four different methods --
quantile, natural breaks, equal interval, and standard deviation.

      My map shows four classification methods - quantile, natural breaks, standard deviation, and equal interval - using population percentage data for residents 65 and older living in Escambia County, Florida. I chose similar graded color ramps for the quantile, natural breaks, and equal interval methods and a divergent color ramp for the standard deviation method. The latter color choice is best for standard deviation as it represents those values closest to the mean as a particular color and as you get farther from the mean in one direction or another they have two different color ramps (in this case reds and blues). I created a custom gradient for the background of the entire map and used drop shadows for the individual method maps. Each map method has a title and a legend.