Data cited at:Numbeo (https://www.numbeo.com/property-investment/rankings.jsp)
Price to Income Ratio is the basic measure for apartment purchase affordability (lower is better). It is the ratio of median apartment prices to median familial disposable income, expressed as years of income.
Mortgage as Percentange of Income is a the ratio of the actual monthly cost of the mortgage to take-home family income (lower is better). Average monthly salary is used to estimate family income. It assumes 100% mortgage is taken on 20 years for the house(or apt) of 90 square meters which price per square meter is the average of price in city center and outside of city center.
Loan Affordability Index is an inverse of mortgage as percentage of income. Used formula is :
(100 / mortgage as percentage of income) (higher is better).
Price to Rent Ratio is the average cost of ownership divided by the received rent income (if buying to let) or the estimated rent that would be paid if renting (if buying to reside). Lower values suggest that it is better to buy rather than rent, and higher values suggest that it is better to rent rather than buy. Our formula to estimate rent per square meter assumes 1 bedroom apt has 50 square meters and 3 bedroom apartment has 110 square meters. It doesn't take into account taxes or maintenance fees.
Gross Rental Yield is the total yearly gross rent divided by the house price (expressed in percentages). Higher is better.