I've been remiss in posting Allison's awesomely thorough wrap up from her class on New York City Cemeteries. Here's the first part, with many more to follow. Enjoy, and don't forget to check out her slideshow of some of the spots mentioned: 

http://www.flickr.com//photos/astrozombie/sets/72157627638485877/show/

From Allison:

Forgotten Cemeteries and Potter’s Fields

In addition to the obvious necropoleis in the five boroughs, there are numerous overlooked burial grounds, some that people walk over every day without knowing of the thousands of dead buried below.

The African Burial Ground in Lower Manhattan holds the remains of 400 Africans buried between the 17th and 18th centuries, although thousands of burials took place there during its use. The remains were found in 1991 during the construction of the Foley Square Federal Office Building and a museum has since been established on the site. However, there is another African Burial Ground under what is now Sara D. Roosevelt Park below Houston Street that has yet to receive any sort of commemoration.

Several public parks were once potter’s fields: Madison Square Park, Bryant Park, and Washington Square Park. All were once on the outskirts of the city and used for burying the unknown or those unable to afford a burial elsewhere. It’s estimated that some 20,000 bodies are still under Washington Square.

New York City’s current potter’s field is on Hart Island on the Long Island Sound east of the Bronx, where bodies are buried in mass graves by inmates from Rikers Island. More than 2,000 of the dead are buried here each year, with about a third being infants or stillborn babies. Severed body parts are also buried in boxes labeled “limbs.” All of the graves are unmarked, except for the isolated burial site of the first child to die of AIDS in New York City. Historic buildings are now being torn down to make room for new burials.

My note: What's a potter's field, you ask? We were wondering about the origins of the term in class, so I went ahead and did some super thorough research on Wikipedia.

Thus: a potter's field is any place where the "unknown or indigent" end up buried. It comes from the Bible--the place strangers were buried was the same place was you mined potter's clay. Since the land was then useless for agriculture, it was, as Wikipedia says, as good a place as any to bury foreigners.

There's also this little "citation needed" tidbit from the Wikipedia page:

Potter's Field was also the name of a small cove of the East River just below the Williamsburg Bridge on the Brooklyn side, where bodies that have been in the river from November through the winter season surface in April as the rising temperature causes them to decompose and rise to the surface. The fluid dynamics of the East River causes a collection of these bodies every year off the docks of Potter's Field.

What?! Go forth and find this place!