Monthly multifamily permit activity has been gyrating like a teenage pop singer of late— rising 17 percent one month, only to fall 8 percent the next. Clearer patterns emerge from an analysis of yearlong, 2010 permit data. That analysis shows where 2011 development activity is likely to be concentrated. Here's a list of the 20 largest markets for multifamily permit activity in 2010, along with percentage increases or decreases.