Geoid vs. Datum — What's the Difference?

The geoid () is the shape that the ocean surface would take under the influence of the gravity of Earth, including gravitational attraction and Earth's rotation, if other influences such as winds and tides were absent. This surface is extended through the continents (such as with very narrow hypothetical canals).

Pl. da·ta (-tə) A fact or proposition used to draw a conclusion or make a decision. See Usage Note at data.

The hypothetical surface of the earth that coincides everywhere with mean sea level.

Pl. da·tums A point, line, or surface used as a reference, as in surveying, mapping, or geology.

The shape, extending through landmasses (continents, etc.), that the surface of the oceans of the Earth would take under the influence of the Earth's gravity and rotation alone, disregarding other factors such as winds and tides; that is, a surface of constant gravitational potential at zero elevation.

(dated) data; a single recorded observation.

(plural: data) (philosophy) A fact known from direct observation.

(plural: data) (philosophy) A premise from which conclusions are drawn.

(plural: datums) A fixed reference point or set of reference points which precisely define a system of measurement or a coordinate system.

(plural: datums) (nautical) A floating reference point, or SLDMB, used to evaluate surface currents in a body of water. Often employed by coastal search and rescue.

To provide missing data points by using a mathematical model to extrapolate values that are outside the range of a measuring device.

Something given or admitted; a fact or principle granted; that upon which an inference or an argument is based; - used chiefly in the plural.

A single piece of information; a fact; especially a piece of information obtained by observation or experiment; - used mostly in the plural.

The quantities or relations which are assumed to be given in any problem.

A point, line, or level surface used as a reference in measuring elevations.

An item of factual information derived from measurement or research