The Robinson projection is a map projection of a world map that shows the entire world at once. It was specifically created in an attempt to find a good compromise to the problem of readily showing the whole globe as a flat image. [1]
The Robinson projection was devised by Arthur H. Robinson in 1963 in response to an appeal from the Rand McNally company, which has used the projection in general-purpose world maps since that time. Robinson published details of the projection's construction in 1974. The National Geographic Society (NGS) began using the Robinson projection for general-purpose world maps in 1988, replacing the Van der Grinten projection. [2] In 1998, NGS abandoned the Robinson projection for that use in favor of the Winkel tripel projection, as the latter "reduces the distortion of land masses as they near the poles". [3] [4]
The Robinson projection is neither equal-area nor conformal, abandoning both for a compromise. The creator felt that this produced a better overall view than could be achieved by adhering to either. The meridians curve gently, avoiding extremes, but thereby stretch the poles into long lines instead of leaving them as points. [1]
Hence, distortion close to the poles is severe, but quickly declines to moderate levels moving away from them. The straight parallels imply severe angular distortion at the high latitudes toward the outer edges of the map – a fault inherent in any pseudocylindrical projection. However, at the time it was developed, the projection effectively met Rand McNally's goal to produce appealing depictions of the entire world. [5] [6]
I decided to go about it backwards. … I started with a kind of artistic approach. I visualized the best-looking shapes and sizes. I worked with the variables until it got to the point where, if I changed one of them, it didn't get any better. Then I figured out the mathematical formula to produce that effect. Most mapmakers start with the mathematics.
The projection is defined by the table: [7] [8] [9]
Latitude | X | Y |
---|---|---|
0° | 1.0000 | 0.0000 |
5° | 0.9986 | 0.0620 |
10° | 0.9954 | 0.1240 |
15° | 0.9900 | 0.1860 |
20° | 0.9822 | 0.2480 |
25° | 0.9730 | 0.3100 |
30° | 0.9600 | 0.3720 |
35° | 0.9427 | 0.4340 |
40° | 0.9216 | 0.4958 |
45° | 0.8962 | 0.5571 |
50° | 0.8679 | 0.6176 |
55° | 0.8350 | 0.6769 |
60° | 0.7986 | 0.7346 |
65° | 0.7597 | 0.7903 |
70° | 0.7186 | 0.8435 |
75° | 0.6732 | 0.8936 |
80° | 0.6213 | 0.9394 |
85° | 0.5722 | 0.9761 |
90° | 0.5322 | 1.0000 |
The table is indexed by latitude at 5-degree intervals; intermediate values are calculated using interpolation. Robinson did not specify any particular interpolation method, but it is reported that others used either Aitken interpolation (with polynomials of unknown degrees) or cubic splines while analyzing area deformation on the Robinson projection. [10] The X column is the ratio of the length of the parallel to the length of the equator; the Y column can be multiplied by 0.2536 [11] to obtain the ratio of the distance of that parallel from the equator to the length of the equator. [7] [9]
Coordinates of points on a map are computed as follows: [7] [9]
where R is the radius of the globe at the scale of the map, λ is the longitude of the point to plot, and λ0 is the central meridian chosen for the map (both λ and λ0 are expressed in radians).
Simple consequences of these formulas are:
The Central Intelligence Agency World Factbook uses the Robinson projection in its political and physical world maps.
The European Centre for Disease Prevention and Control recommends using the Robinson projection for mapping the whole world. [12]
The Mercator projection is a conformal cylindrical map projection first presented by Flemish geographer and mapmaker Gerardus Mercator in 1569. In the 18th century, it became the standard map projection for navigation due to its property of representing rhumb lines as straight lines. When applied to world maps, the Mercator projection inflates the size of lands the further they are from the equator. Therefore, landmasses such as Greenland and Antarctica appear far larger than they actually are relative to landmasses near the equator. Nowadays the Mercator projection is widely used because, aside from marine navigation, it is well suited for internet web maps.
In cartography, a map projection is any of a broad set of transformations employed to represent the curved two-dimensional surface of a globe on a plane. In a map projection, coordinates, often expressed as latitude and longitude, of locations from the surface of the globe are transformed to coordinates on a plane. Projection is a necessary step in creating a two-dimensional map and is one of the essential elements of cartography.
The transverse Mercator map projection is an adaptation of the standard Mercator projection. The transverse version is widely used in national and international mapping systems around the world, including the Universal Transverse Mercator. When paired with a suitable geodetic datum, the transverse Mercator delivers high accuracy in zones less than a few degrees in east-west extent.
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The Kavrayskiy VII projection is a map projection invented by Soviet cartographer Vladimir V. Kavrayskiy in 1939 for use as a general-purpose pseudocylindrical projection. Like the Robinson projection, it is a compromise intended to produce good-quality maps with low distortion overall. It scores well in that respect compared to other popular projections, such as the Winkel tripel, despite straight, evenly spaced parallels and a simple formulation. Regardless, it has not been widely used outside the former Soviet Union.
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The equidistant conic projection is a conic map projection commonly used for maps of small countries as well as for larger regions such as the continental United States that are elongated east-to-west.
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The central cylindrical projection is a perspective cylindrical map projection. It corresponds to projecting the Earth's surface onto a cylinder tangent to the equator as if from a light source at Earth's center. The cylinder is then cut along one of the projected meridians and unrolled into a flat map.
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In the cartography of the United States, the American polyconic projection is a map projection used for maps of the United States and its regions beginning early in the 19th century. It belongs to the polyconic projection class, which consists of map projections whose parallels are non-concentric circular arcs except for the equator, which is straight. Often the American polyconic is simply called the polyconic projection.
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This map features the Winkel Tripel projection to reduce distortion of land masses as they near the poles.