Jersey City is about 20 times smaller than New York City.

New York City (including all five boroughs: Manhattan, Brooklyn, Queens, The Bronx, and Staten Island) is approximately 781 sq km, while Jersey City (map shows its 11 named neighbourhoods; the area covers the whole city) is approximately 38 sq km, making Jersey City 4.89% the size of New York City.
Tip: This to-scale comparison of New York City vs. Jersey City uses the Mercator projection, which distorts the size of regions near the poles.
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