The Köppen climate types is a typing of climate. Goyder's Line is a dichotomy of climate. Some scientist expert took Goyder's line and created a generality from that particular: climates with more than 250mm of rain (all else equal) are Mediterranean, and climates with less that 250mm of rain (all else equal) are dry semi-arid.
So somehow, somebody took a list of yes-no questions ("does this area receive 250mm of rain or no," "does this area receive mean 200 hours of sunshine or no,"...) and inferred generalities from them. Say by looking at a sample size of 20,000 areas and evaluating them according to those yes-or-no questions and looking for generalities based how the land areas were evaluated by those yes-or-no questions taken as an aggregate.
But this is so tedious that there has to be an automated way of inferring generalities given a list of binary options and a population.
So somehow, somebody took a list of yes-no questions ("does this area receive 250mm of rain or no," "does this area receive mean 200 hours of sunshine or no,"...) and inferred generalities from them. Say by looking at a sample size of 20,000 areas and evaluating them according to those yes-or-no questions and looking for generalities based how the land areas were evaluated by those yes-or-no questions taken as an aggregate.
But this is so tedious that there has to be an automated way of inferring generalities given a list of binary options and a population.