The ocean is of paramount importance to our planet and its inhabitants. It covers more than 76% of the Earth's surface. It plays a crucial role in regulating the Earth's climate, acting as a large heat sink and distributing heat through ocean currents. Furthermore, it produces over half of the planet's oxygen, supporting the breathing of terrestrial and marine organisms. But how much do we know about the ocean? More than 80% of our ocean is still unmapped, unobserved, and unexplored, leaving most of our planet unknown to us. Moreover, the ocean is the main driver of climate and influences human activity in numerous ways. As a result of increasing human activity, the oceans have become overburdened and teetering on the brink of permanent decline. At this stage, it is critically important that our oceans be preserved for the existence of mankind. So, we must know the ocean in-depth to avert a catastrophic situation in the future. Hydrography is that knowledge or applied science which is essential to know for the preservation of the ocean.