I wonder how do javascript engines optimize hash table lookups. Especially since it is faster to access a member of an object than to access a variable of an outer function. It seems to me that the former requires a hash table lookup with a string key while the later suffices with a pointer into the closure of an outer function and the offset of the variable.

At first I thought the color scale meant the gravity pull at the ground level. But then it may also mean the distance of a point on the gravitational geoid shape from the center. The two explanations are not equivalent. So which is it?