> ...I'm still not sure what gravity is, but it must be based more on mass rather than size; because of the fluctuation in earth's gravity.

Well, yes. The Newtonian formula for gravitational force (between two masses, each concentrated in a point) is:

       m1 * m2
F = G ---------
         r^2

Here, G is a constant (the gravitational constant), m1 and m2 are the masses (typically expressed in kg.) and r is the distance between them (typically expressed in meters).

So, you see, the force increases when the masses are greater. The force also increases when the distance is reduced.

BTW, for spheres, with their mass evenly distributed, the resulting force is the same as if all the mass were distributed in the center.

Any uneven distribution of mass within the Earth would have an effect on its gravitation on nearby objects, for example, on satellites.

Back to the "size" issue: Let's say our Sun would collapse into a black hole. That would reduce its diameter from ca. 1.3 million km. to about 3 km., IIRC. If the Sun didn't lose mass in the tranformation (or perhaps acquire new mass, from nearby objects), then its gravitational pull on the Earth would not change, either. The Earth might continue going around the invisible black hole, in the same orbit it currently has. (That is, assuming that it wasn't somehow affected during the transition.)

The force of the gravitational pull, then, depends on the distance and on the masses involved, but on no other factor.