Borders of the oceans (maritime boundaries)

Where are the borders of the oceans? We call these the maritime boundaries. Technically our planet only has one ocean: the giant, not-so-creatively named “world ocean.” But that makes it hard to talk about different parts of the ocean on different parts of the planet. It makes sense to split it up, but how do you divide a continuous body of water? Since we humans have a habit of making things all about us, historically we have divvied up all that water based on our own perceptions.