Interesting to see how much Portland spiked in the last decade, from ~3 to >5. I wonder how much of the surrounding area that includes? I've seen housing prices skyrocket in Portland, but much less so in surrounding areas. (They've still increased, but I'd hypothesize that they haven't increased nearly as much as within Portland. I'd love to see separated data to check that hypothesis, though.)
It looks like they're using a metro region. If you take a look at their "county crosswalk" [1] data that might give more information about it. For example NYC is "MetroRegionID_Zillow" 394913 that has a corresponding "RegionID" in the price to income dataset.
I've seen articles showing Portland and Seattle increasing 10+% per year for the last 4 years. So yeah. Not sure what specifically is going on in portland though. Hear about Seattle tech a lot more.
Some choice datapoints:
I think the national average is around 3.1 and around 3.0 is considered "healthy" (your mortgage costs about 3x your yearly income).[1] http://www.zillow.com/research/data/
[2] http://files.zillowstatic.com/research/public/Affordability_...