Manhattan (NYC borough) is 29 times larger than Monaco.
Area: 2 km2 World Factbook
Population: 30,508 (July 2014) World Factbook
Monaco, officially the Principality of Monaco, is a sovereign city-state and microstate, located on the French Riviera in Western Europe. It is bordered by France on three sides; one side borders the Mediterranean Sea. Wikipedia
Area: 59 km2 calculated
Manhattan is the most densely populated of the five boroughs of New York City. The borough is coterminous with New York County, an original county of the U.S. state of New York. Wikipedia