The colours indicate the relative efficiency of the given nation in comparison to all other nations with regard to cereal production when taking agropotential and nitrous oxide emissions into account. The darker the colour, the more efficient a countries cereal production.
Computation of agropotential: We start with three data sets. The first one contains the agropotential per grid cell, the second one tells whether there is arable land in this grid cell or not, and finally, the third one maps grid cells to countries. We loop over the grid cells accumulating the agropotential of grid cells containing arable land into each country, and eventually, compute the average agropotential per country out of it.
Analysis:
Data Envelopment Analysis (DEA) is applied with nations as decision making units (DMU). The inputs of the DMUs are agricultural nitrous oxide emissions and agropotential, while the output is cereal yield. Thus, the computed efficiencies are a relative measure of efficiency of these nations regarding the production of cerial with respect to their available agropotential and the emitted nitrous oxide emissions.