Statistical Method
To distinguish among importance categories on the composite map we used a classification system based on standard deviation units from the mean pixel value for the town. Our goal was to identify which regions of Coventry had exceptionally high levels of co-occurring resources.We first computed the average value of all of the pixels in the final composite map. We then computed the difference between every pixel's value and the town average; the units of the difference are standard deviations units. Pixels that have standard deviation unit differences less than 0 (i.e. negative numbers) have fewer co-occurring resources than the town average. We ignored these. Pixels that have a positive standard deviation difference have more co-occurring resources than average.
The darkest green pixels (very critical class) on the composite map are 2 or more standard deviation units from the town average and represent the highest 2.5 percent of the area of the town for co-occurring resources. The middle shade (critical class) of green represents the top 16% of the town for co-occurring resources and the light green (important) represents areas in town that have more co-occurring resources than the town average.
We adopted a statistical definition of critical resource regions because it is objective and free from any human bias.
