My question is what is the reference for the elevation of the terrain? Obviously on Earth it is sea level, but what is it on Mars? So, to Wikipedia I go, and:
Quote:
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Zero elevation: Since Mars has no oceans and hence no 'sea level', a zero-elevation surface or mean gravity surface must be selected. The datum for Mars is defined by the fourth-degree and fourth-order spherical harmonic gravity field, with the zero altitude defined by the 610.5 Pa (6.105 mbar) atmospheric pressure surface (approximately 0.6% of Earth's) at a temperature of 273.16 K. This pressure and temperature correspond to the triple point of water.
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Also, interesting to point out that the elevation difference between the highest and lowest points on Mars is much greater than the difference here on Earth between Mt. Everest and the Mariana Trench.