The above is a 2D histogram of y and z internal coordinates describing the positions of C-alpha atoms involved in hydrogen bonds between antiparallel Beta-strands.
There is no color coding. It is given as it is.
What can we assume about the data points if a histogram is circular?
When does a histogram take a circular shape?
[Note: "2D histogram" is a synonym for what bioinformaticians typically call heat maps, see here]
