The New York Times blog has a zoomable digital copy of the NYPD's map. Popular stereotypes of the various ethnic groups labelled on the map help explain why they were charted out. Germans (Kraut spies), Russian Jews (Commies), and Italians (mobsters) are the first three groups on the map. Other groups leave me wondering why they were even bothered with: Scandinavians (blondes a big threat in the 1910s?) and French (I seriously do not know why the French were feared).
The Times' blogger points out that ethnic mapping continues to be very controversial. The FBI recently received harsh negative press for its geographical monitoring of American Muslim communities. What many people ignore; however, is that normal census data can be and is used to do detailed racial, social, and economic mapping for police departments, academics, and even private companies to name just a few.