In a bivariate contour (density) plot of height versus weight, the shape and orientation of the elliptical contours reveal the correlation structure between the two variables. Elongated contours tilted so that their major axis runs between the 'short and heavy' and 'tall and light' corners (rather than between 'short and light' and 'tall and heavy') indicate that the two variables are not simply positively correlated in the naive sense across the whole population, and in particular that the population density is higher along that diagonal, meaning there are more tall-and-light individuals than tall-and-heavy individuals.