Except that looking at a single year doesn't tell you much about why even a ratio of 3 isn't good in SF. After a quick google search I came across this set of charts that do a pretty good job of covering the history of population and housing in SF.[0] For the period 2010-2013, population rose 32,500 and housing expanded 7,500 - a sustained ratio of 4.33. The decade prior to that saw a much gentler ratio just a little over 1, but that may have been catching up to the booming growth of the '90s and the dotcom bubble. The thing that really caught my eye though was the tidbit of information in the first chart - nearly half of the existing housing in SF was built prior to 1940. The original report (linked in the article) provides a much more grim outlook for 2010-2015 predicting a total population growth of 60,000 with a housing increase of 12,000 - a ratio of 5.[1]

0 - http://sf.curbed.com/2015/2/4/9995388/sfs-population-is-grow...

1 - http://www.paragon-re.com/San_Francisco_Real_Estate_Feb_2015