Architecture of New York City spread outward from where it originally began at the southern-tip of Manhattan Island into surrounding areas. In order to house the burgeoning population, farm land and open space in Upper Manhattan, the Bronx, Queens, Brooklyn, and Staten Island were developed into neighborhoods of brownstones, apartment buildings, multi-family and single-family homes. The density of this new construction generally depended on the area's proximity and accessibility to Manhattan. The development of these areas was often spurred by the opening of bridges and the connection of boroughs via public transportation. For example, the Brooklyn Bridge was completed in 1883 and connects Brooklyn and
Staten Island Tunnel funded by the city, the tunnel was expected to help expand the then-sparsely populated borough in a similar manner to the population and development explosions seen in Brooklyn and the Bronx. Under the Dual Contracts, three routes were proposed—two to Brooklyn and one to Manhattan—which would connect the Staten Island Railway's rapid transit service (SIRT) to existing subway lines. The Manhattan proposal, often called the "direct route," would have connected with the Interborough Rapid Transit Company (IRT)'s lines under Battery Park, near the current Brooklyn–Battery Tunnel. "Direct Route A" would have utilized a five-section tunnel under the New York Harbor,