how do they determine how high land is above sea level in a landlocked area?

Question

forgive me if its obvious, but how do they tell how high they are from sea level if there is no sea nearby, do they compare the land to surrounding areas that are close to water
or is there another measurement
for instance how would you tell if nebraska or some such state was a certain measurement above sea level?

Morningfox · Accepted Answer

Now surveyors use GPS to get altitude.  Before that, they used barometers. Since air pressure changes with the weather, the air pressure had to be corrected for temperature, and averaged for many weeks or even months or years.

poornakumar b · Answer

About a hundred and fifty years ago, the British ruling administration organised a 'Great Triangulation Survey' of India lasting several years. An extensive system of benchmarks all over the country was the result. The most visible feature is that every railway station's platform is a 'benchmark' with the height marked at lower corners in small letters, on the massive rectangular plaque displaying the station's name[New Delhi:'+228.048 mtrs MSL']. They were able to estimate the heights of all Himalayan peaks. This is how height of Mt.Everest (in the land-locked kingdom of Nepal, then) was estimated. These were confirmed (with minor errors) afterwards by improved methods of surveying from satellites etc. Dam construction too needs this vital information.

? · Answer

Air pressure, standard AP is 14.7 PSI @ sea level and decreases linear.
 Taking AP at any spot will give you the local altitude, every city or airport has 1 OFFICIAL altitude.

Shantanu · Answer

they probably use a BAROMETER....which tells them the pressure at a certain height which they compare to the pressure at sea level (76cm of mercury)..and the difference gives the height of that place above the sea level,,,

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how do they determine how high land is above sea level in a landlocked area?

4 Answers