Standard APA guides will help with articles and other standard sources. However, some statistical/data resources are not as likely to be useful for psychology-related pursuits, so you will need to interpret the guidelines to write adequate citations. I suggest some of the following formats for data from SimplyMap (without the proper indentation):
Geographic Research. (2012). Map based on Median Household Income, from Census data, downloaded February 28, 2013, from from http://www.simplymap.com/
Geographic Research. (2012). SimmonsLOCAL data retrieved February 28, 2013, from http://www.simplymap.com/
Note that the author is Geographic Research. They are the publishers of Simply Map even though that is hard to tell in the actual database. Simply Map as the author may also be acceptable. For more help, the following guides (developed by librarians) provide additional examples and tips for sources like Simply Map, American Factfinder and other similar resources. They are all just examples and they may not necessarily all agree, so use what works best for you (and your instructor) and be consistent.