DoubleDot7 t1_ixxid8i wrote

That's a great response. One thing to add: sea levels rise and fall over relatively short timescales, geologically speaking, which can greatly affect coastal map shape.

For example, 40,000 years ago, during the last ice age, sea levels were lower. Thus, there was solid land between Siberia and Alaska (Beringia land mass), and the British Isles and the Netherlands. Our current coastal regions were inland regions, and what is now submerged land was once the coast. In some areas, such as southern Africa, this could mean that the coast was several hundred kilometers further out than it is today. Islands such as New Zealand would have been bigger and possibly connected, too.

On the other hand, if sea levels keep rising, we may have to remove parts of Florida, New York, California and many island nations from maps over the coming decades and centuries.