tongfen: The least common geography

TongFen is a Chinese term referring to the conversion of two fractions to the least common denominator. It is also the name of an R package, tongfen, created by Jens von Bergmann to reconcile shifting geographic boundaries across years, primarily for census data.

This is a common problem. You want to compare census data, voting patterns, or some other geographic measure across time, but discover that the subunits do not quite line up. Maybe some of them merged, or they split, or someone simply redrew the boundaries a little nicer. The package helps you work out what happened and resolve the resulting conflicts. It makes a frustrating and manual process a little smoother.