Equal Area (Histogram) Distribution

Equal Area (Histogram) Distribution calculates the colour breaks so that there are approximately the same number of data samples in each bin colour, resulting visually in a map where each colour covers roughly the same area. However, the Equal Area default behaviour (indicated with a contour interval of 0) will yield bin boundaries that are not nice, rounded numbers. If you would like to round the bin boundary values to nice numbers, simply enter the rounding multiplier as the contour interval. The contour interval takes precedence over the number of bins; as a result, the number of bins may decrease.

Zone Colour Ranges using Equal Area (Histogram) Distribution

For this method, the histogram of the data distribution is calculated, and the number of zones is translated into percentile (‰) equivalent breaks. Then, the data is binned into their percentile equivalents.

How it works:

Given N+1 distinct colours, N data breaks are required. First, the histogram is calculated, from which the equivalent values for the percentiles100/N, 2*100/N, 3*100/N, …. (N-1)*100/N are extracted and set as the bin boundaries. Then the data is binned and displayed in the corresponding colour.

For example, if the number of colours N is 11, the equivalent value of the 10th, 20th, 30th, 40th percentiles become the consecutive bin boundaries.

Percentile equivalent ‰

Example: Bin boundary rounding

Initially the calculated bin boundary values may have many decimals (values on the left in table below). You can round them off to a multiple of 0.5 (on the right) by providing a contour interval of 0.5:

08.178374           08.00

09.538242           09.50

11.026232           11.50

12.941288          13.50

14.856344            16.00

17.231992         18.50

20.344588            22.00

23.457183            26.50

 …

Example: Bin boundary rounding may result in fewer bins

In the colour table below, the column to the left is calculated by default for 21 colour levels. The middle column represents the same data calculated with the contour interval of 0.5; this results in 17 colour levels.