A temporal reference system defines how time is measured and expressed in a dataset — the time equivalent of a coordinate reference system for space. It establishes the origin time is counted from, the units it is counted in, and the calendar or clock convention in use, so that a timestamp means the same thing to everyone reading it.
The main kinds
- Calendar and clock systems — dates and times expressed in a recognised calendar, such as ISO 8601 timestamps in UTC.
- Temporal coordinate systems — elapsed time measured from a defined epoch, such as Unix time counting seconds from 1 January 1970.
- Ordinal systems — named, ordered intervals without fixed numeric length, such as geological eras.
Why it matters in location data
Movement data is meaningless without reliable time. Joining observations into a trajectory, applying a dwell-time threshold, or comparing a campaign period against a control period all assume every timestamp shares one reference. Mixed time zones, inconsistent handling of daylight saving, or a mixture of local and UTC timestamps will corrupt any sequence-dependent analysis — and will do so quietly.
In standards
ISO 19108 defines temporal schema for geographic information, setting out how temporal reference systems are described alongside the spatial ones in a GIS.
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