Two satellites fly around the earth and they measure each other to see how their orbits change. The variations indicate differences in gravitational pull due to landmasses and densities. Crazy! India has some of the least gravity in the world, about 1% less than average. That's a lot!
Finally, we pulled up a document with this:
In truth, these differences in gravity can have an effect on shipping. Imagine 10 000 metric tons of food being shipped to or from Norway. A difference of 0.1 % makes a difference of 10 000 kg in weight. If the shipment is valued at $1/kg, that's a $10,000 difference in price, just because of gravity. Weird.