Flatlands is a neighborhood in the southeast part of the borough of Brooklyn in New York City. The current neighborhood borders are roughly defined by the Bay Ridge Branch to the north, Avenue U to the south, Ralph Avenue to the east, and Flatbush Avenue to the southwest.

Brooklyn is a borough of New York City. Located on the westernmost end of Long Island, it is coextensive with Kings County in the U.S. state of New York. With 2,736,074 residents as of the 2020 United States census, Kings County is the most populous of the five boroughs of New York City and the most populous county in the State of New York. The population density of Brooklyn was 37,339.9 inhabitants per square mile (14,417.0/km2) in 2022, making it the second-most-densely-populated county in the United States, behind Manhattan, and it had the ninth-highest population of any county nationwide. Were Brooklyn still an independent city, it would be the fourth most populous in the U.S. after the rest of New York City, Los Angeles, and Chicago.