Polsby-Popper 4 pi A / P^2, Schwartzberg P / (2 sqrt(pi A)),
convex-hull ratio and Reock (area over the minimum enclosing circle, by
Welzl's incremental algorithm on the hull vertices) of a simple polygon.
References
Polsby, D. D. and Popper, R. D. (1991). The third criterion: compactness as a procedural safeguard against partisan gerrymandering. Yale Law and Policy Review 9, 301-353.
Reock, E. C. (1961). A note: measuring compactness as a requirement of legislative apportionment. Midwest Journal of Political Science 5, 70-74.
