While the Vatican City is the center of the Catholic Church and home to St. Peter's Basilica, it's not the biggest Catholic church in the world.
St. Peter's Basilica is the largest church in the world by volume, but the biggest Catholic Church by area is the Basilica of Our Lady of Aparecida in Brazil.
It's important to note that the Vatican City is a sovereign city-state and not just a church. The Vatican Church is the central administration of the Catholic Church, and it is located in Vatican City.
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