Reduced level notation

A height calculated against a stated datum.

Also known as: RL notation, Calculated level notation

Engineering & technicalMaps & navigationQuiet profile

Meanings

A reduced level is a height calculated relative to a stated datum, distinguished from a staff reading, which is a measurement taken against an instrument.

Common modern usageVerified fact
Gives a height relative to a stated datum, calculated rather than read directly.
Contexts: Maps
Common modern usageVerified fact
Is meaningless without its datum, which is why a level book states the datum once and every figure in it inherits that statement.
Contexts: Maps

Visual description

A figure printed on a drawing or in a level book, given to three decimal places and labelled with its datum.

A fuller structured visual breakdown is not yet documented for this symbol.

Confidence

IdentityModerate confidence: Moderate confidence because the identity is documented in encyclopedic references, but only a single source has been found so far.
Historical originLow confidence: Low confidence because the historical origin is documented in encyclopedic references, but only a single source has been found so far, but early or supporting evidence is limited, but the regional or cultural match to this specific claim is not precise.
Current useModerate confidence: Moderate confidence because the current use is documented in encyclopedic references, but only a single source has been found so far.
Visual matchModerate confidence: Moderate confidence because the visual match is documented in encyclopedic references, but only a single source has been found so far.

Sources

Surveying: methods, control and setting out
Wikipedia · retrieved 2026-08-24
Tertiary reference. Used for the marks and notations of control networks, traverses and setting out, and for what each is for. Not used for any procedure or accuracy claim.

Last reviewed 2026-08-24

Help improve this page

Meanings

A reduced level is a height calculated relative to a stated datum, distinguished from a staff reading, which is a measurement taken against an instrument.

Common modern usageVerified fact

Gives a height relative to a stated datum, calculated rather than read directly.

Contexts: Maps

Common modern usageVerified fact

Is meaningless without its datum, which is why a level book states the datum once and every figure in it inherits that statement.

Contexts: Maps

Confidence

IdentityModerate confidence: Moderate confidence because the identity is documented in encyclopedic references, but only a single source has been found so far.
Historical originLow confidence: Low confidence because the historical origin is documented in encyclopedic references, but only a single source has been found so far, but early or supporting evidence is limited, but the regional or cultural match to this specific claim is not precise.
Current useModerate confidence: Moderate confidence because the current use is documented in encyclopedic references, but only a single source has been found so far.
Visual matchModerate confidence: Moderate confidence because the visual match is documented in encyclopedic references, but only a single source has been found so far.