Re: I'm certain you don't mean to say that the gravity on earth is the same everywhere on earth.
There are very minor gravitational variations in both magnitude and direction, caused by the departures of the geoid from a perfect sphere, or because of differences in subterranean mass concentrations and relief (causing different distances from the center of the earth), but they are the sort of thing that can only be measured by very sensitive measurements. Centrifugal acceleraton due to earth's rotation also plays a role, as do probably the lunar tides, but nothing like 3%.
From your link I see there is a relative low in the vicinity of the BT, but there are others scattered all over the earth's surface as well.