It's about 200,000 times as big as Grand Central Station.
In other words, the size of Grand Central Station is 0.00000500 times 31,000,000 dunams.(formally Grand Central Terminal, a.k.a. Grand Central, a.k.a. GCT) (New York City, New York) (total terminal area). Grand Central station, the largest train station in the world by platform count, measures 200 dunams in total area. The large flag which was suspended from the concourse ceiling following the September 11th 2001 terrorist attacks measures about 0.07 dunams.
It's about 250,000 times as big as The Pentagon.
In other words, 31,000,000 dunams is 225,000 times the size of The Pentagon, and the size of The Pentagon is 0.000004440 times that amount.(a.k.a. United States Department of Defense Headquarters) (Washington, D.C.) (total floor area)
The Pentagon, the world's largest office building, contains a total floor area of 138 dunams. Built during World War II, the designers compensated for the steel rations then in effect by using 310,000 cu. m of concrete in the construction efforts.
It's about 300,000 times as big as Ellis Island.
In other words, 31,000,000 dunams is 279,000 times the size of Ellis Island, and the size of Ellis Island is 0.000003580 times that amount.(Jersey City, New Jersey and New York City, New York)(now officially part of the Statue of Liberty National Monument)
Ellis Island, home of the Ellis Island Immigration Station, is 111 dunams in total area. Nine-tenths of the island were artificially created after the New York-New Jersey borders had already been defined, leading to a sovereignty dispute which was settled by the US Supreme Court in 1998.
It's about 350,000 times as big as Alcatraz.
In other words, the size of Alcatraz is 0.00000290 times 31,000,000 dunams.(a.k.a. The Rock) (California)
Alcatraz Island measures 89 dunams. It is known a part of the Golden Gate National Recreation Area, and has historically served as a lighthouse, fort, military prison, and — most famously — a federal prison.
It's about 400,000 times as big as Buckingham Palace.
In other words, the size of Buckingham Palace is 0.00000250 times 31,000,000 dunams.(a.k.a. Buckingham House) (Westminster, London, England)
Buckingham Palace, the official residence of the British monarch, contains about 77 dunams of total floor space. The palace was first inhabited by Queen Victoria in 1831, although after the death of her husband in 1861, the Queen endeavored to spend as little time there as public opinion would allow.
It's about 600,000 times as big as Windsor Castle.
In other words, 31,000,000 dunams is 580,000 times the size of Windsor Castle, and the size of Windsor Castle is 0.00000170 times that amount.(Windsor, England) (total site area)
One of the official residences of the British monarch, Windsor Castle measures about 53 dunams. It is the largest inhabited castle in the world and is also the oldest in continuous use, having been occupied since it was built by William the Conqueror about 900 years ago.
It's about 600,000 times as big as a Polo field.
In other words, 31,000,000 dunams is 617,928.1910 times the size of a Polo field, and the size of a Polo field is 0.000001618311020 times that amount.(for field polo) (United States Polo Association rules; unboarded side maximum)
An outdoor polo field must measure 274.32 m in length and 146.304 m to in width for a total playing area of up to 50.16764160 dunams. Polo traces its origins to an Iranian (then Persian) war game from the 5th Century, which was played with as many as 100 players per side.