Map projections and distortion
Flattening Earth's curved reference surface requires a choice of distortions.
Key knowledge
A map projection assigns positions on a curved Earth reference surface to a plane. Over finite curved regions, a flat map cannot preserve every distance, area, shape and direction simultaneously. Equal-area, conformal and equidistant projections preserve different specified properties; equidistant does not mean that every pair of mapped points has its true distance.
Conditions and scope
- Select a projection and scale appropriate to the region and measurement; local small-area errors may be small even when global distortion is large.
- Projection properties apply to the chosen reference surface and parameters. A projection alone does not specify or transform the underlying geodetic datum.
Sources · 3
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
- GEOG 486, Projection properties: Equivalent, Conformal and EquidistantCary Anderson and Fritz Kessler · Penn StateTextbook chapter
- How are different map projections used?U.S. Geological SurveyReference guide
- A Guide to Coordinate Systems in Great Britain, v3.6 (2020), §§1.2 and 3.1Ordnance SurveyReference guide · PDF
Evidence and review
Directly inspected Penn State's opening and Equivalent, Conformal and Equidistant bodies on distortion, local angles, area–shape tradeoffs and distance preservation only from specified points or lines. Also read the indexed complete USGS FAQ answer; direct HTML extraction did not expose it and the poster PDF returned 403. OS coordinate-system distinctions constrain the datum clause. Excludes the FAQ's overbroad 'only Mercator' direction wording and a spherical great-circle shortcut for all ellipsoidal geodesics.
2026-10-10 · Independent Mathematics and Information editor (/root/core_math_information). Independent AI editorial review of this entry's statements, equations, applicability conditions and source coverage. Source checks apply to these claims within their stated limits.
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