One common way to measure affordability is to look at the cost of things relative to local incomes. But the world is getting increasingly more complicated than this. Here, for example, is an interesting article talking about the "nomadification" of cities such as Medellín.
What this is referring to is digital nomads who might work for and draw a salary from a company in say the US, but who work fully remotely in places like Medellín, Buenos Aires, and Mexico City. It's like working from home all the time, except home is some exciting city in Latin America.