# Difference between revisions of "Dictionary:Map projection"

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A scheme for displaying the Earth’s curved surface on a plane surface. Some of the more common projections are shown in Figure [[Special:MyLanguage/Dictionary:Fig_M-4|M-4]]. Distortions of one sort or another are inevitable. <b>Equivalence</b> is the projection property wherein the product of orthogonal scale factors is maintained constant so that areas are preserved. <b>Conformality</b> is the property wherein angles are preserved. <b>Standard lines</b> are great or small circles along which the scale is uniform and constant. (<b>a</b>) <b>Tangent projections</b> are projections onto a surface (plane, cylinder, or cone) that is tangent to the Earth; (<b>b</b>) <b>secant projections</b> are those made onto a surface that intersects the Earth. (<b>c</b>) A <b>transverse projection</b> has its axis perpendicular to the Earth’s axis (sometimes merely at any angle to the Earth’s axis). (<b>d</b>) An <b>azimuthal projection</b> is onto a tangent plane; distortions increase as the distance from the point of tangency. (<b>e</b>) A <b>stereographic projection</b> is both azimuthal and conformal. (<b>f</b>) A <b>polyconic</b> has a straight central meridian and each parallel is the arc of a circle and is standard; the scale along meridians is therefore variable and the map is neither equivalent nor conformal. <b>(g) Transverse Mercator projections</b> (onto a cylinder at right angles to the Earth’s axis) and [[Special:MyLanguage/Dictionary:Lambert_conic_projection|''Lambert conic projections'']] (q.v.) form many official coordinate systems; the [[Special:MyLanguage/Dictionary:Universal_Transverse_Mercator_(UTM)|''Universal Transverse Mercator'']] (q.v.) is one standard system in widespread use. <b>(h)</b> A <b>Robinson projection</b> permits some distortion in size at high latitudes to maintain shapes at middle and low latitudes. | A scheme for displaying the Earth’s curved surface on a plane surface. Some of the more common projections are shown in Figure [[Special:MyLanguage/Dictionary:Fig_M-4|M-4]]. Distortions of one sort or another are inevitable. <b>Equivalence</b> is the projection property wherein the product of orthogonal scale factors is maintained constant so that areas are preserved. <b>Conformality</b> is the property wherein angles are preserved. <b>Standard lines</b> are great or small circles along which the scale is uniform and constant. (<b>a</b>) <b>Tangent projections</b> are projections onto a surface (plane, cylinder, or cone) that is tangent to the Earth; (<b>b</b>) <b>secant projections</b> are those made onto a surface that intersects the Earth. (<b>c</b>) A <b>transverse projection</b> has its axis perpendicular to the Earth’s axis (sometimes merely at any angle to the Earth’s axis). (<b>d</b>) An <b>azimuthal projection</b> is onto a tangent plane; distortions increase as the distance from the point of tangency. (<b>e</b>) A <b>stereographic projection</b> is both azimuthal and conformal. (<b>f</b>) A <b>polyconic</b> has a straight central meridian and each parallel is the arc of a circle and is standard; the scale along meridians is therefore variable and the map is neither equivalent nor conformal. <b>(g) Transverse Mercator projections</b> (onto a cylinder at right angles to the Earth’s axis) and [[Special:MyLanguage/Dictionary:Lambert_conic_projection|''Lambert conic projections'']] (q.v.) form many official coordinate systems; the [[Special:MyLanguage/Dictionary:Universal_Transverse_Mercator_(UTM)|''Universal Transverse Mercator'']] (q.v.) is one standard system in widespread use. <b>(h)</b> A <b>Robinson projection</b> permits some distortion in size at high latitudes to maintain shapes at middle and low latitudes. | ||

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## Latest revision as of 21:06, 20 March 2017

A scheme for displaying the Earth’s curved surface on a plane surface. Some of the more common projections are shown in Figure M-4. Distortions of one sort or another are inevitable. **Equivalence** is the projection property wherein the product of orthogonal scale factors is maintained constant so that areas are preserved. **Conformality** is the property wherein angles are preserved. **Standard lines** are great or small circles along which the scale is uniform and constant. (**a**) **Tangent projections** are projections onto a surface (plane, cylinder, or cone) that is tangent to the Earth; (**b**) **secant projections** are those made onto a surface that intersects the Earth. (**c**) A **transverse projection** has its axis perpendicular to the Earth’s axis (sometimes merely at any angle to the Earth’s axis). (**d**) An **azimuthal projection** is onto a tangent plane; distortions increase as the distance from the point of tangency. (**e**) A **stereographic projection** is both azimuthal and conformal. (**f**) A **polyconic** has a straight central meridian and each parallel is the arc of a circle and is standard; the scale along meridians is therefore variable and the map is neither equivalent nor conformal. **(g) Transverse Mercator projections** (onto a cylinder at right angles to the Earth’s axis) and *Lambert conic projections* (q.v.) form many official coordinate systems; the *Universal Transverse Mercator* (q.v.) is one standard system in widespread use. **(h)** A **Robinson projection** permits some distortion in size at high latitudes to maintain shapes at middle and low latitudes.