Although their titles range from location scout to urban planner, the participants of "Block By Block: New York Street Historians," a photo-lecture event set for Sunday at the Brooklyn media-arts center UnionDocs, all have one thing in common.

"They're each out there on foot exploring these obscure corners of New York and coming back with their own observations about what they've seen," said Nathan Kensinger, filmmaker and curator of the event.

The roots of this homegrown blend of vocation and avocation can be traced back to journalist George Foster's after-hours city walking tour "New York By Gaslight," published in 1850. ...