What is the relationship between Median Income and Median Price?

[Ramsey Blankenship]

What is the happy medium for me as in an investor in regards to a city's affordability for its tenants.

For instance - Austin, Tx. has steady increases in job growth, substantially increasing the population, raising the median household income, ultimately driving up the median home prices 61% over the last 16 years.  What does this mean for me - The city of Austin. Tx is doing amazing! - So amazing, it's unaffordable :(

Cities such as Shreveport, La. and Montgomery, Al. have decreased their population over the past 16 years, having the opposite effect making homeownership affordable for its tenants. What this means for me - Affordable properties with high vacancy rates :(

So - What is the happy medium? If I find a city with a healthy increase in job growth, population, and median household income - how can I understand if it will likely be a rental market which will cash flow.

Please note that I understand picking up the phone and calling professionals in the area is the best way to get the ground truth.  I am trying to understand data and trends from a Macro perspective. 

Ramsey