|Modifying the Style with a FeatureStyleModifier / Range Theme|
You can create ranges using five methods:
Equal Count has the same number of records in each range. If you want to group 100 records into 4 ranges using Equal Count, the Equal Count method computes the ranges so that approximately 25 records fall into each range, depending on the rounding factor you set.
When using Equal Count (or any other range method), it's important to watch out for any extreme data values that might affect your thematic map (in statistics, these values are referred to as outliers).
Equal Ranges divides records across ranges of equal size. For example, you have a field in your table with data values ranging from 1 to 100. You want to create a thematic map with four equal size ranges. The Equal Ranges method produces ranges 1-25, 25-50, 50-75, and 75-100. (Since ranges use "=>" and "<=", they need to overlap.)
Keep in mind that the Equal Ranges method may create ranges with no data records, depending on the distribution of your data.
Natural Break creates ranges according to an algorithm that uses the average of each range to distribute the data more evenly across the ranges. It distributes the values so that the average of each range is as close as possible to each of the range values in that range. This ensures that the ranges are well-represented by their averages, and that data values within each of the ranges are fairly close together. The Natural Break algorithm is based on the procedure described by Jenks and Caspall in their article "Error on Choroplethic Maps: Definition, Measurement, Reduction" from the Annals of American Geographers, June 1971.
When you create ranges using Standard Deviation, the middle range breaks at the mean of your values, and the ranges above and below the middle range are one standard deviation above or below the mean.
Quantiling enables you to build ranges that determine the distribution of a thematic variable across a segment of your data. For example, you can quantile state population by urban population to illustrate how urban population is distributed across the United States. Your map legend will not indicate that you have used Quantile to build your ranges. You can customize the map legend so that it shows which field you used to quantile the table.
Spectrum™ Technology Platform also suppports creating custom ranges. To set ranges manually, use Custom.