"Area deformation on the Robinson projection". The American Cartographer. 16 (4): 294–296. doi:10.1559/152304089783813936. ↑ From the formulas below, this can be calculated as 1.3523 0.8487 ⋅ 2 π ≈ 0.2536 {\displaystyle {\frac {1.3523}{0.8487\cdot 2\pi }}\approx 0.2536} . ↑ European Centre for Disease Prevention and Control.