This is what America's gun crisis looks like

Your analysis is incomplete. Most of the NYC mass shooting locations are specified by borough. An incomplete list for NYC is:

Aug 28, 2015 Brooklyn, NY; Aug 3, 2015 Brooklyn, NY; Aug 2, 2015 Brooklyn, NY; Jul 20, 2015 Bronx, NY; Jun 24, 2015 Manhattan, NY; Jun 15, 2015 Brooklyn, NY; Jun 13, 2015 Bronx, NY; May 4, 2015 Bronx, NY; Apr 27, 2015 Brooklyn, NY; Feb 1, 2015 Manhattan, NY; Jan 24, 2015 Queens, NY; Nov 30, 2014 Brooklyn, NY; Oct 18, 2014 Brooklyn, NY; Sep 19, 2014 Queens, NY; Sep 1, 2014 Brooklyn, NY; Aug 17, 2014 Queens, NY; Jul 28, 2014 New York, NY; ... and I stopped.

I also question the usefulness of listing the 13 matches for "Los Angeles" the city and leaving out the urban area. There were 5 mass shooting in Long Beach, 1 in Santa Monica, 3 in Pomona, etc.