There's a thing going around among people that should know better about how, on Jan. 4, we'll all suddenly weigh a lot less because of a weird planetary alignment. Apparently, the gravitational effects of our Solar System neighbors will be so suddenly huge that we'll be able to experience weightlessness or something close. It's really a resurrected April Fool's joke, but one well-attuned to the internet fake-satire landscape.
That said, gravity on Earth is not a uniform thing. In 2005, a group of researchers at the German Research Centre for Geosciences in Potsdam released what's affectionately known as the Potsdam Gravity Potato, which is just Earth. (Via NASA APOD.)
Using data collected by the then-new satellites GRACE and CHAMP, both of which are designed to collect observations about the planet's gravitational and magnetic fields along with climate data, the Potsdam group was able to map out Earth's gravity-scape with an entirely new level of precision. And said field looks like a lumpy potato.
The 2011 update is below:
In the images, areas with slightly higher gravitational fields are shaded red and raised in elevation, while those with slightly lower fields are shaded blue and lowered. The key word here is slightly. The average acceleration due to gravity on Earth is 9.80665 m/s2, and the variation across the entire planet's surface is usually within .7 percent of that. At the surface of the Arctic Ocean it's about 9.8337 m/s2, while in Mexico City it's 9.766 m/s2. The significance of that variation is easy enough to work out on paper.
These slight variations have to do with either differences in topography, like mountain ranges, or differences in internal density. So, the Himalayan Mountains have a bit more pull than the bottom of the Indian Ocean, but some differences aren't as obvious.