sciencewords:

A lot of people have been mislead by a post that talks about the “lumpy” Earth, and unfortunately it seems that people genuinely believe the Earth is this shape. As one person pointed out, we have images of the Earth from space, and while it would be disingenuous to refer to it as a perfect sphere, it very much is spherical. A rudimentary reverse Google image search tells me that the image in the misleading post is a simulation of the Earth without water… which is just plain wrong.

In fact, the shape you’re seeing is a geoid, which is a simulation of what Earth would look like if you neglected the influence of anything other than rotation and gravity. A geoid is a dynamic equipotential surface, which means that every point on the surface has the same gravitational potential.

Since it was recently NASA’s Astronomy Picture of the Day, this seems like a good opportunity to talk about a geoid that is something more than a context-less gif: the Potsdam Gravity Potato, pictured above. It’s the result of efforts by a group at Helmholtz Centre Potsdam to create a highly detailed map of the Earth’s gravitational field. Like in a heat map, red elevated levels indicate stronger gravitational effects, and depressed blue levels indicate that they’re lower. The potato-like shape occurs due to the Earth’s uneven gravitational field. This is why high places such as the Himalayas coincide with local maxima on the geoid—but of course not all maxima and minima are the result of noticeable physical features; the Earth has inhomogeneous variations in its density, which account for much of the gravitational difference.

For further reading, check out this article.