Dempsy, New Jersey, is fictional. It is modeled, however, upon Jersey City, a very real place. In order to give you some idea of what Dempsy might be like, I'm providing illustrations of one of the zip codes in Jersey City. I chose it because it includes a waterfront development similar to the one in which Ray Mitchell lives as well as areas similar to those where the other characters reside.
Zip Code 07302, Air view courtesy of Google Earth. The tower to the bottom right would be similar to that described in Samaritan. A view to the southeast would include the Statue of Liberty. Click on the link above to get sensusdata for the area.
Note the street pattern here. You'll see that some of the areas described in economic or social terms are outlined by the changes in street orientation.
Click on the Picture to open a view from Google Earth. Google Maops Maps offers a chance to see the part of JerseyCity similar to where Ray Mitchell used to live and where he lives when the story occur.
To get a sense of the neighborhoods in Dempsey (Jersey City) Click on the map to the left. The neighborhood map at City-Data.com seems to be down, but the neighborhood data is available.