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Datum (geodesy)

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This is an old revision of this page, as edited by Cferrero (talk | contribs) at 10:06, 14 February 2003 (Removed redirect as datum is a distinct entity in some sciences). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

In geology, geography, cartography, surveying and other disciplines, a datum is a reference surface against which measurements can be made.

For instance, sea-level is commonly used as a datum against which height (or depth) of topographic features can be measured. Whilst the use of sea-level as a datum is useful for geologically recent topographic features, it should be remembered that sea-level has not stayed constant throughout geological time (see Vail-curve).

On maps, heights and depths will typically be given in height above datum or depth below datum. Ordnance Survey maps define the Orndance Survey Datum or OSD which is usually sea-level, but should be checked in the map legend.

Datum is also the singular for data.

External link: [Ordnance Survey]

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