Definition
A GPS position fix that provides latitude and longitude only, without a reliable altitude value. It is computed when the receiver can use signals from only three satellites, which is the minimum needed to solve for horizontal position but not enough to also solve for vertical position.
Plain English
A GPS fix that tells you where you are on the map, but cannot tell you how high you are.
Context Anchor
Seen in Global Positioning System discussions when describing the kind of position fix a receiver can provide.
Derivation
Two-dimensional refers to the two horizontal dimensions — north-south and east-west — that locate a point on a flat map. Adding altitude (up-down) would make it three-dimensional. The term tells you exactly what is missing: the third dimension.
Why Pilots Care
Indicates whether a GPS receiver is supplying only horizontal location or a full three-dimensional fix that includes altitude for vertical navigation and obstacle clearance.
Analogy
It is like a pin on a flat map. The pin can show the building you are in, but it does not show which floor you are on.
Intuition Check
Do not assume “position” always includes altitude. Here, two-dimensional position means horizontal location only; height is not part of the fix.
Example Sentence 1
When the GPS dropped to a two-dimensional position, the pilot continued to navigate laterally but used the altimeter for altitude.
Example Sentence 2
Until the receiver locked onto enough satellites for altitude, the display remained limited to a two-dimensional position.