Altitude vs elevation vs height

Start with the zero

The reference surface carries more meaning than the everyday label.

Vertical position is a distance from somewhere. A summit might be described relative to a mapped sea-level datum, a mathematical ellipsoid, the ground immediately below, or the bottom of the mountain. All four descriptions can use the word height, yet they produce different numbers.

In technical work, height is the broad term. It can mean the distance between the top and bottom of an object, or the distance from a point to a named reference surface. A geodetic height is measured from a reference ellipsoid. An orthometric height is related to a gravity-based surface called the geoid. These are not two spellings for the same measurement.

Outdoor apps often use altitude and elevation more loosely. That is workable when the unit, source and reference remain consistent, but the word alone cannot tell you how the figure was obtained. When two products disagree, compare their vertical references before treating either one as an error.

Mapped ground

Elevation usually describes mapped ground height above a recognised datum.

Topographic mapping commonly uses elevation for the orthometric height of the land. Contours join places assigned the same elevation, while spot heights identify selected points. In Great Britain, familiar mainland mapping heights are connected to Ordnance Datum Newlyn rather than to the WGS 84 ellipsoid used by satellite positioning.

Above sea level is a useful shorthand, not a complete geodetic definition. Sea level moves with tides, weather and ocean circulation. A national datum provides a stable realised reference, tied to observations and control rather than resetting whenever the water changes.

Contextual language

Altitude is useful, but its reference still needs to be stated.

Altitude is widely used for the vertical position of an aircraft, person or device. Depending on the context, it may refer to a sea-level-based datum, an ellipsoid, local ground or a pressure-derived level. Aviation distinguishes these references because the operational consequences matter. Consumer route products may simply label a chart axis altitude.

The label does not prove that a phone measured the value directly from satellites. A device or service may combine satellite positioning, a barometer, calibration data and a terrain model. An imported GPX file may already contain elevation values from an earlier process. By the time the number reaches a route card, its original method may no longer be visible.

Four checks

Ask what was measured, from where and for what purpose.

• Read the unitMetres and feet can be converted. A unit conversion does not change the datum.
• Find the referenceLook for a vertical datum, geoid model, ellipsoid or an explicit above-ground reference.
• Identify the sourceSeparate a recorded device height from a value sampled later from terrain data.
• Match the purposeA route overview can tolerate generalised terrain that would be unsuitable for surveying or engineering.

The route views in the beacen Library provide planning context, not a survey certificate.

When metadata is unavailable, describe the number modestly: The app reports 620 metres is more accurate than claiming a surveyed summit elevation. A displayed height cannot reveal its measurement method by itself.