The Nazis located their ghettos on the sites of the old Jewish quarters.

Evidence

Tragically, that was not to be the last chapter in the history of the Jewish ghettos of Europe. During World War II, the Nazis collected Jews in ghettos before rounding them up for transportation to the death camps. This ghettoization was more readily accomplished in Eastern than in Western Europe in part because the Eastern Jews were a more closely knit identifiable group than their Western counterparts. The Nazis established their ghettos on the site of the old Jewish quarters, thereby confirming a continuity with the old order. Indeed the Nazis themselves distinguished between 13 Polish “ghettos” that were completely sealed and a larger number of “Jewish quarters” that were closely guarded but were not fully enclosed. — David Theo Goldberg, John Solomos, A Companion to Racial and Ethnic Studies, 2382