Working with shuffles we establish a close link between Kendall's tau, the
so-called length measure, and the surface area of bivariate copulas and derive
some consequences. While it is well-known that Spearman's rho of a bivariate
copula A is a rescaled version of the volume of the area under the graph of A,
in this contribution we show that the other famous concordance measure,
Kendall's tau, allows for a simple geometric interpretation as well - it is
inextricably linked to the surface area of A.Comment: 12 pages, 3 figure