We've explored such a small part of the ocean that we know more about the moon and Mars. This new three-dimensional map can help us get more acquainted with the body of water that occupies most of our planet, though. It sorts water masses around the world into 37 categories of different temperatures, salinity, oxygen and nutrient levels. There are other maps out there, but they mostly focus on surface or coastal ecosystems. This project, which is officially called ecological marine units (EMUs), includes the waters between the surface and the ocean floor. It maps the frigid waters of the deep sea, the oxygen-deprived Black Sea, the Red Sea and even some rivers in the Northern Hemisphere.