map projection
Let an agent explain what map projections are and what each preserves or distorts, help choose a projection for a purpose, relay standard definitions and codes from geodetic references, and separate projections from datums and coordinate reference systems.
Research draft, second pass
A second pass drafted this model: the structure a model of this thing needs, and what is known about it in the world. The line under this one says how the second half was obtained - researched against sources, or recalled without web access, in which case nothing here was read anywhere and every claim is a lead to verify. Unreviewed either way.
written by Claude from model knowledge without web access - no source was read, every claim is a lead to verify
Researched by: Claude
Purpose and description
Let an agent explain what map projections are and what each preserves or distorts, help choose a projection for a purpose, relay standard definitions and codes from geodetic references, and separate projections from datums and coordinate reference systems.
A systematic method for representing the curved surface of the Earth or another body on a flat map, defined by mathematical rules that map latitude and longitude to plane coordinates; every projection distorts some combination of area, shape, distance or direction, and projections are chosen by purpose, such as Mercator for navigation, equal-area for thematic maps and conformal for surveying.
What it is for: Representing a curved surface on a flat map.
It can be explain how projections work and what they distort; identify a projection from its properties; help choose a projection for a purpose; relay codes and parameters.
Distinguishing features
Mathematical mapping from sphere or ellipsoid to plane
Always distorts something
Classified by surface, aspect and property
Chosen by purpose
What it looks like
Not visible in itself; seen in the shape of the graticule and continents on a map.
Physical character
properties preserved: at most one of area, shape, or true distance along all lines property - no projection preserves all
How it is recognised
Graticule shape: straight, curved or converging meridians and parallels
Preserved property: area, shape, distance or direction
A datum and a coordinate reference system are separate concepts
Related models
is a kind of - a mathematical mapping
is part of - with a datum and units
is used in - the discipline
is confused with - the reference surface, not the projection
In practice
Families and kinds
cylindrical projections such as Mercator and equal-area cylindrical
conic projections such as Lambert conformal conic and Albers
azimuthal projections such as stereographic and orthographic
pseudocylindrical and compromise projections such as Robinson and Winkel tripel
polyhedral and interrupted projections
projections by property: conformal, equal-area, equidistant
Identifiers
EPSG code numeric for projected coordinate reference systems
PROJ string text parameters for software
Standards and regulation
ISO 19111 spatial referencing by coordinates
EPSG geodetic parameter dataset
National mapping agency standards
Failure modes and hazards
Misreading area on Mercator maps
Mixing projections without transformation
Confusing projection with datum
Political disputes over map appearance
Also called
Where this came from
wikidata · CC0 1.0
Drafted structure
Bundle to layer to finding to question, as the second pass will find it: 4 bundles · 8 layers · 8 findings · 16 questions.
Concept What a projection is.
Definition.
Definition
Definition and distortion.
Definition
Definition.
- What is a map projection, and why must every projection distort something? definition
- Is the question about the projection, the datum or the coordinate reference system? boundary
Classes
Classification.
Classes
Classes.
- How are projections classified by surface, aspect and preserved property? definition
- Which entry fits a specific projection? action
Choose Choosing a projection.
Practice.
Purpose
Purpose and choice.
Purpose
Purpose.
- Which projection suits navigation, thematic mapping, surveying or world maps, and why? action
- What region and scale is the map for? boundary
Distortion
Measuring distortion.
Distortion
Distortion.
- How is distortion measured and visualised, for example with Tissot indicatrices? measurement
- Which references are standard? provenance
Use Parameters and software.
Use.
Parameters
Parameters and codes.
Parameters
Parameters.
- What parameters define a projected coordinate system, and where are codes published? provenance
- Which entry fits coordinate reference systems? action
Transform
Transformation.
Transform
Transform.
- How are data transformed between projections in software? action
- Which entry fits GIS software? action
Context History and debate.
Context.
History
History.
History
History.
- How did projections develop from Ptolemy through Mercator to modern compromise projections? provenance
- Which entry fits the history of cartography? action
Debate
Debates.
Debate
Debate.
- What debates exist about world map projections and their perceived bias, with positions attributed? provenance
- Is the presentation neutral? boundary
What the second pass must settle
- Should each named projection be a separate entry?
- How should EPSG codes be linked?
- The registry entry has merged aliases for specific projections and map orientations; should they be split off?