Definition
A geodetic reference system, adopted in 1983, that defines the precise mathematical model of the Earth used to calculate latitude and longitude positions across North America. It is the standard horizontal datum used by the FAA for aeronautical charts, instrument procedures, and navigation databases, and is functionally equivalent to the World Geodetic System of 1984 (WGS 84) for practical aviation purposes.
Plain English
A standard agreed-upon model of the Earth's shape that all charts, GPS units, and navigation systems use so that a given latitude and longitude points to the same spot for everyone.
Context Anchor
Seen in chart legends, including en route chart legends, where the chart identifies the reference system used for its plotted positions.
Derivation
A 'datum' in surveying is a fixed reference used as the starting point for measuring positions. 'North American Datum of 1983' simply means the reference system established in 1983 for North America, replacing the earlier 1927 version (NAD 27). Knowing this clarifies that NAD 83 is just the agreed starting point everyone measures from, not a piece of equipment.
Why Pilots Care
Using the correct datum prevents small but operationally significant position errors when plotting intersections or entering waypoints.
Analogy
It is like agreeing on the same zero mark before measuring with a ruler. If two people use different starting marks, their measurements may not line up exactly.
Intuition Check
NAD 83 is not a route, fix, or navigation aid. It is the chart’s position reference system—the basis for where charted latitude and longitude points are placed.
Example Sentence 1
The chart legend notes that all geographic coordinates are referenced to NAD 83, so positions agree with the GPS receiver.
Example Sentence 2
GPS receivers in the aircraft were set to NAD 83 to match the chart data.