Data is for the code for this website.

Churn rate is the number of commits for a file.
Cyclomatic complexity is a count of the linearly independent paths through source code in a file - the number of decisions encoded within that file.
Upper left: cowboy region
(complex code that didn't grow incrementally).
Upper right: rats nest
(re-factor these first)
Lower left: healthy closure Lower right: fertile ground
(incubators for new abstractions)

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Churn rate was calculated with git churn.
Cyclomatic complexity was calculated with complexity-report for javascript files; with radon for python files.