The geographic distribution of deviations from the relationship between plant family richness and net primary productivity (taken here from the published values modelled by Uchijima & Seino) can be investigated by overlaying estimates for the two in two separate colours. The example uses green for plant family richness and blue for the productivity scores, so that black grid cells on the map show low values for both, white shows high values for both, grey shows similar values for both (these scores lie on the diagonal of the colour key, to the upper right), green shows an excess of plant families over productivity, and blue an excess of productivity over plant families (Spearman correlation coefficient rho= 0.85) (below):