As a Papist, my hackles are in semi-raised position anytime Margaret Sanger is the subject, but looking at the map of PP locations, I couldn't help noticing they were located in the country's most intense concentrations of Catholics. And I couldn't help remembering how much she hated the Church.
I know there's another hypothesis that probably explains the data just fine—that Catholics historically tend to concentrate the big cities. My tinfoil hat was made in NYC's Garment District.