A photo essay.

In Camden, N.J., perhaps the poorest American city I regularly visit, I photograph what I call paired houses: two dwellings, side by side, one occupied, the other empty. Those living in the occupied home often have their lives made more difficult by what happens on the other side of a shared wall. If I see a neighbor or meet the resident of one of the occupied houses, I ask how they're coping. They tell me that people throw trash in the front and back yards of the vacant unit, causing foul smells and attracting rats. Physical problems in the empty shell cause accelerated decay in the occupied house. Water may be left running in the unoccupied unit, causing moisture to migrate next door. In cold weather, pipes burst. Joists rot and collapse, tearing bricks out of the shared wall. And if the empty dwelling is not properly sealed, prostitutes and drug addicts may break in and start fires.

If a resident of a middle-class neighborhood dies or moves to a nursing home, or if a dwelling burns, the empty house is usually guarded or secured by the owner's family. The police keep an eye out for it. Neighbors, well-aware of the impact of a deteriorating eyesore on property values, alert city officials whenever they see a house falling into disrepair. The situation is quickly brought under control.

It's different in a crumbling inner city like Camden. Even Walt Whitman's old house at 328 Mickle St.—the only home he ever owned—was by the 1980s adjacent to a vacant three-story dwelling and just two houses away from a ruin. House values in Camden are low and likely to remain so since the population of the city is declining, unemployment is high, and there is little new demand for houses. The number of vacant houses is likely to increase; many will eventually be acquired by the city, which is too poor either to board them up or to demolish them.

As if afraid to disappear anonymously, people who live adjacent to abandoned homes are actually more likely to decorate the fronts of their houses during holidays than those who live more securely.