NASA Blue Marble satellite composite of Earth in an equirectangular global map.

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Preparing the 3D view

Preparing lighting and the first complete frame…

Model scale

Globe → flat map. ±85° latitude. projection distorts length, shape or area.

Mercator · 0% unfolded. Mercator is conformal locally; area grows strongly towards the poles. Gold circles start with the same angular radius on the globe; compare their shape and area on the flat map. Intermediate shapes are a visual interpolation.

Map projections

Compare how map projections represent a curved Earth on a flat surface, identifying the distortions each introduces.

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Why it happens

A map projection transfers positions from a curved surface to a plane. Every projection distorts some combination of area, shape, distance and direction, so the right choice depends on the map’s purpose.

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NASA Blue Marble Next Generation, July 2004. A cloud-free satellite composite in a latitude–longitude grid: the map stretches high latitudes and is not equal-area.

Try a comparison

Flatten each projection fully. Compare the equal-sized circles at low and high latitudes, then describe the trade-off between area and shape.

Reading the result

Judge each projection when it is fully flat; intermediate shapes are a visual transition rather than a separate projection.

A common misunderstanding

One flat world map can preserve every area, shape, distance and direction.

Flattening Earth’s curved surface necessarily introduces distortion. A projection may preserve a selected property, such as area, while changing others. Compare a map with a globe and choose its projection according to the task, rather than assuming all visual comparisons are equally reliable.

Cases

Exam language

Projection

A mathematical method for representing positions on a curved surface on a flat map. Every world projection changes some combination of area, shape, distance or direction. Its suitability depends on which properties matter for the map’s intended use.

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NASA Blue Marble monthly composite in an equirectangular latitude–longitude grid. Latitude measures angular distance north or south of the equator; parallels run east–west. The geographic reference lines are mathematical, not marks on the land.

Mercator

A conformal cylindrical map projection on which constant compass bearings plot as straight lines. It is useful for some navigation tasks, but areas become greatly enlarged towards the poles. Apparent land areas on it should not be compared directly.

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NASA Blue Marble imagery reprojected by Mdf into Mercator. Local angles are preserved, area grows towards the poles, and a constant-bearing route plots as a straight line.

Equal-area

Describing a projection that preserves the relative areas of regions on a map. Shapes and angles must be distorted to achieve this on a flat surface. Equal-area maps are useful when comparing the size or distribution of geographic regions.

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NASA satellite imagery reprojected by Strebe into Mollweide. This equal-area projection preserves relative areas but distorts shapes; the ocean has been lightened for legibility.

Conformal

Describing a map projection that preserves local angles and small shapes. This is useful for bearings, but area can become strongly distorted over a world map. A conformal projection cannot also preserve the area of every region.

Rhumb line

A path of constant compass bearing, shown as a straight line on a Mercator map. Except for special cases, it is not the shortest path on a sphere.

Gores

Tapered strips of a map designed to be fitted around a globe; small strips reduce the distortion needed to cover a sphere.

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Library of Congress: Hondius terrestrial globe gores, reissued by Giuseppe di Rossi in 1615. This is a scan of a real cartographic object; the tapered paper strips were designed to fit a spherical globe. Its historical geography is not a modern reference map.

Compromise projection

A map projection that balances several kinds of distortion without preserving any one property exactly everywhere.

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NASA satellite imagery in Robinson projection. This compromise projection balances several distortions; it preserves neither all areas nor all local angles.

Distortion

A change in area, shape, distance or direction caused by projecting a curved surface onto a plane. No flat world map preserves all of them everywhere.

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