The pillar is said to be about 2000 ft wide and stretches from the floor to the ceiling of the great cavern of Sshamath, about a mile high.
Here is what we have in game now,


Uploaded with ImageShack.us
I placed the drow raider there to give a perspective of the total size. Now compare that to a XY plane to scale (2000 ft wide) but only 1/2 Z plane to scale (about 2640, half a mile), the maps have a limited height,




Remember, that is only half as tall as it should be because of toolset limitations. Imagine if you had to walk up that every time you wished to leave the city.
Another thing to think about is how long it takes you to get from point A to point B ingame. From Baldur's Gate to Beregost is approximately 160 miles in a strait line. If you were to run at 10 miles an hour, a decent jogging speed, it would take you 16 hours to arrive at your location. So we say 5min real time equals 1 hour game time. That is still 80 minutes to run from Baldur's Gate to Beregost in game.
Just something to think about while you wondering around ingame.