How is altitude measured - i.e. the height of mountains?

Question

I live in a town calculated as 900 ft above sea level, but have been in mountains 7,000 ft above sea level - who does this measuring?

Answer 1

The measuring is normally done with an altimeter. Because it measures atmospheric pressure relative to the pressure at sea level it is actually a barometer. The higher you go, the lower the pressure and therefore the greater the differential. The altitude is then calculated from this differential.

Answer 2

It can either be done by triangulation from the ground or by satellite (more common these days). Ground-based triangulation uses a line-of-sight with the mountaintop being measured from a point at a known altitude and measuring the angle of that line with a level one and using a little trig (knowning how far away you are from the mountain). The same trick works from space, but uses lasers to measure distances between the satellite, the mountaintop and some fixed reference point (like the home office from where the satellite is controlled). It tends to be a little more accurate, because the angle and distance measurements are calibrated to be a bit more precise.

Answer 3

They use sea level as a base and measure by triangulation.