Housing affordability is measuring the cost of housing that is normalized over income. It is a better measurement of affordability than housing cost alone because it takes into account how much money people make and if they can actually afford a house based on what they earn yearly. It also makes it more accurate to compare the affordability of two cities, especially with sizeable population differences.
The four main housing affordability categories represented in this map are: affordable, moderately unaffordable, seriously unaffordable and severely unaffordable. There is also a No Data category to represent the areas where census data was not gathered. The affordability rating categories were determined by the 11th Annual Demographia International Housing Affordability Survey. In my opinion they can be “trusted” because they are assigned using the median multiple which is consistent internationally over the years.
Affordability overall is a good measure of a city’s livability because it indicates if the average person can afford certain goods and gives an idea of how the city is doing in terms of poverty. However, there are still a lot of other factors that influence livability, but would not be reflected in the affordability and it is important to keep that in mind when doing such evaluations.