Why build up when you can build down? I think building into a mountain would be best so long as there was stability. Mt. Everest is less than 6 miles high, a 50 mile high pyramid would be like building 1000s of mountains and probably take a considerable amount of time to build. Building a mega city from scratch to be like a pyramid with many structures supporting larger structures to contain the vacuum tube at the center would be necessary to have any kind of economic feasibility. I'd just dig as deep a hole as possible and then top it off with a conventional structure to get it a little bit higher. Better yet, build it into a mountain from some old mine shafts that could be used to load the shuttles. Initial vacuum or near vacuum could be achieved by pumping water melted from the ice cap into the tube which would be deeper (or just terminate into a much less narrow space at its depth) than the volume of water used and contain a drain plug. Vacuum generators could then be used to top off the vacuum and be powered by a series of hydroelectric turbines from ice melt and a bunch of nuclear reactors (lots of energy required to reach escape velocity) which would serve dually as the power for the electromagnetic propulsion. Near the tip of the pipe a high speed "vacuum damn" would be engaged just prior to another one opening at the top to release the payload thus preserving as much vacuum as possible. A series of these "damns" could be used to allow larger or smaller payloads and provide backups in case one fails to close. The magnetic system would continue post vacuum to ensure the change in air pressure wouldn't misdirect the payload. Much smaller rocket stages would then be used to achieve the 25,000+ miles per hour escape velocity required. Breaking inertia wastes a lot of energy.
It looks like all of the largest mountains are in east Asia, so it looks like it will be China, India, or Russia who will have the skill and best mountains for it. Though I guess having a high plateau is more important than peaks, so it it's probably a bit harder to determine where the best launch site would be. I could think of a few more unconventional means requiring much less energy too. Don't forget there are limits to how many Gs a human body can endure. I think that's why we have roller coasters. I imagine they boost bone and tissue density.
Oh, hey Cliff, check this out: http://www.longecity...00-mile-radius/