Why have maps changed throughout history?

Maps have changed throughout all of history because many explorers and other people have new places that were unknown to man before. In fact in 1507, Martin Waldseemüller created a new map which included "America" as a separate continent. The separate continent idea came from Amerigo Vespucci's. America is just a Latinized version of Amerigo.

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It does! As well as changes brought by exploration, as said above, equally important changes have been improvements in accuracy, especially in the development of projections to solve the problem of representing a spherical planet on a flat surface. Other major developments were of grid systems so locations can be described by co-ordinates, and of course in surveying techniques.