Government agencies can be good sources of information on urban planning. The ones listed below would be useful if you are investigating the Greater Boston area; to find one for your city, see the search tips below.
If you can't find what you are looking for using a website's own navigation, try site: searching! Also called "domain searching," this is a method you can use to search all the pages within one web domain (e.g., brandeis.edu).
Search engines including Google and Duck Duck Go support the following search syntax: housing site:sf.gov
This would search the entire website of the city of San Francisco (sf.gov) for the word "housing."