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Description (Specifications)[edit]

Altitude (or height) is defined as the distance above a reference datum of a point or object.

n.b. this term is not used to describe the geographical height of land surfaces above that datum, the term elevation being preferred instead

History & Background (Dossier)[edit]

The key to understanding Altitude is the understanding of the reference datum used. This is complex because the centre of mass of a body may not be an equal distance from the surface of that body. Historically, on Terra and Vland, the reference datum was typically Mean Sea Level. This level varied between poles and equator because of the planets' spin and varied from actual sea level because of tides, air-pressure differences, etc. Under various circumstances and for particular purposes, the datum might be defined as the sea or land surface itself or as a specific atmospheric pressure.

When other planets were surveyed and colonised, the term mean sea-level could be wholly inappropriate. Planets often have no water to form seas (e.g. Mars or Lirshaia); they may have no solid or liquid surface at all (e.g. Gas Giants). In these cases, a specific point on the land surface (not always the lowest point) or a specific atmospheric pressure might be set as the reference instead.

Astrogation/Navigation Officers should always take care to note the local definition of altitude's reference datum lest they discover that the defined zero altitude is well below the local land or sea surface.

References & Contributors (Sources)[edit]

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