It's acity with lots of renters some of whom, when they move, leave a big pile of stuff outside their apartment building.

If the stuff includes books, I look at them. I often take not just books that appeal to me but others, so I can leave the others in laudramats, on top of trash cans, on public benches.

I figure many more people are willing to look at and many adopt books left in publc singly or by two than are willing to dig in a big pile. In a city with lots of readers, books are easy to move by making a simple move or two.