@siracusa @atpfm Correct use of “the mainland” spotted in this street atlas (John Tauranac, “Manhattan Block by Block”, 2005) that I picked up at a used bookstore over the weekend.
@kjhealy @siracusa @atpfm Except part of New York County (Manhattan) is also on the mainland. https://en.wikipedia.org/wiki/Marble_Hill,_Manhattan
Marble Hill, Manhattan - Wikipedia

A collection of sf objects and related tibbles for making maps of New York City

Simple features boundary files for New York City across various administrative and Census geographies.