Porcupine Pete

I'm Porcupine Pete and I love geography.
Did you know that five hundred years ago people thought the planet Earth was flat as a pancake?
Today we know Earth is round, but it's not a perfect sphere either.
In fact, it's not even an ellipsoid because of its varied and irregular surface.
The shape of our planet can best be described as a "geoid".
Bet you didn't know that!