I am trying to determine which on Earth's surface has the lowest gravity. Googling is not finding anything concrete. My natural inclination would be to think of Mount Chimborazo in Ecuador, being on the equator (centripetal force) and also being the furthest point from the Earth's center. However, the GRACE gravity map has the area listed in red for high gravity, presumably due to local mineral anomalies or mantle structure.
Lowest gravity on earth surface is near Sri Lanka based on the articles below.
The new gravity maps revealed the variations of free-fall gravity over Earth were much bigger than previously thought.
Earth's gravitational pull is smallest on the top of the Huascaran mountain in the South American Andes, and largest near the North Pole.
According to http://en.wikipedia.org/wiki/Gravity_of_Earth#Comparative_gravities_in_various_cities_around_the_world Mexico City has the lowest gravity of any city. However the article doesn't mention mountain tops.
One of the places with lower gravity is Hudson Bay, Canada, and this explains why and how that works:
Sri Lanka and south India has least gravity level on the earth. As you say this is almost the equatorial region and this area has minimal gravity as measured by the SriLankan government. the point on the Earth's surface with the lowest gravity is hiriwadunna in Sri Lanka www.map.google.com
Probably Mt. Chimborazo has the MOST gravity, as being in the "fattest" part of the planet and as one of the highest mountains you will have LOTS of mass generating more gravity (remember the more mass, the more gravity).