We know that the Gemara (I don't know where) states that Yerushalayim is the highest point of the Earth. Now, any survey of the surrounding hills will show that this cannot be taken literally at face value. Some say that it means that Yerushalayim in the highest spiritual place on the Earth. This is indeed correct, but I think one can show a more literal meaning to this.
If we look at the Earth as a perfect sphere, the "highest" point will obviously be the "top" of the sphere. However, since the Earth is in space, every point can be seen as the "top" - it all depends on one's orientation.
Now, another idea I have heard on this topic, is that Yerushalayim is the center of the civilized world, or that it is the center (or top) of the Earth's land mass.
I do not know of anyone who has performed a scientific center-of-mass calculation of all land masses on Earth to come up with a spot which is the "top".
However, with the help of Google Earth, we can see a nice result of this idea, at least visually.
Here is a picture of the Earth, positioned so that the Holy of Holies is directly at the center (marked here by the glowing yellow dot):
[For you techy types it is roughly at (31 46' 41" N) (35 14' 06.6" E)]
Now using an online tool (or simple math), we can calculate the exact opposite spot on Earth from this location, and we see that the Earth centered on THAT spot looks like this:
[It is at: (31 46' 41" S) (144 45' 51" W)]
Interesting, no? The opposite of Yerushalayim in smack dab in the middle of the Pacific Ocean, thousands of miles away from the nearest continent!
So, we see that there can be a possible literal meaning to the idea that Yerushalayim in indeed at the highest point on Earth, when land mass in considered.
(If anyone wants to take the time to calculate the true center of mass on a sphere, be my guest - be sure to give weighting to populated areas).