Definitions html://egsc.usgs.gov/isb/pubs/MapProjections/projections.html

1. Definitionshtml://egsc.usgs.gov/isb/pubs/MapProjections/projections.htmlDefinitionshtml://egsc.usgs.gov/isb/pubs/MapProjections/projections.html • Azimuth • —The angle measured in degrees between a base line radiating from a center point and another line radiating from the same point. Normally, the base line points North, and degrees are measured clockwise from the base line.

2. Aspect • —Individual azimuthal map projections are divided into three aspects: the polar aspect which is tangent at the pole, the equatorial aspect which is tangent at the Equator, and the oblique aspect which is tangent anywhere else. (The word "aspect" has replaced the word "case" in the modern cartographic literature.)

3. -Almucantar Graticule lines that correspond to meridians of the normal projection is called verticals and paralles of the normal projection is called almucantars

4. Conformality • —A map projection is conformal when at any point the scale is the same in every direction. Therefore, meridians and parallels intersect at right angles and the shapes of very small areas and angles with very short sides are preserved. The size of most areas, however, is distorted.

5. Developable surface • —A developable surface is a simple geometric form capable of being flattened without stretching, shrinking or tearing • Many map projections can then be grouped by a particular developable surface: cylinder, cone, or plane.

6. Equal areas • —A map projection is equal area if every part, as well as the whole, has the same area as the corresponding part on the Earth, at the same reduced scale. No flat map can be both equal area and conformal.

7. Equidistant • —Equidistant maps show true distances only from the center of the projection or along a special set of lines. For example, an Azimuthal Equidistant map centered at Washington shows the correct distance between Washington and any other point on the projection. It shows the correct distance between Washington and San Diego and between Washington and Seattle. But it does not show the correct distance between San Diego and Seattle. No flat map can be both equidistant and equal area.

8. Graticule • —The graticule is the spherical coordinate system based on lines of latitude and longitude.

9. Great circle • —A circle formed on the surface of a sphere by a plane that passes through the center of the sphere. The Equator, each meridian, and each other full circumference of the Earth forms a great circle. The arc of a great circle shows the shortest distance between points on the surface of the Earth.

10. Linear scale • —Linear scale is the relation between a distance on a map and the corresponding distance on the Earth. Scale varies from place to place on every map. The degree of variation depends on the projection used in making the map.

11. Map projection • —A map projection is a systematic representation of a round body such as the Earth or a flat (plane) surface. Each map projection has specific properties that make it useful for specific purposes.

12. Rhumb line • —A rhumb line is a line on the surface of the Earth cutting all meridians at the same angle. A rhumb line shows true direction. Parallels and meridians, which also maintain constant true directions, may be considered special cases of the rhumb line. A rhumb line is a straight line on a Mercator projection. A straight rhumb line does not show the shortest distance between points unless the points are on the Equator or on the same meridian.

13. Cylindric: Projections in which the meridians are represented by a system of equidistant parallel straight lines, and the parallels by a system of parallel straight lines at right angles to the meridians. • Pseudocylindric: Projections in which the parallels are represented by a system of parallel straight lines and the meridians by concurrent curves.

14. Conic: Projections in which the meridians are represented by set of straight lines and the parallels by concentric circles. • Pseudoconic: Projections in which the parallels are represented by concentric circular arcs, and the meridians by concurrent curves. • Polyconic: Projections in which the parallels are represented by a system of nonconcentric circular arcs with their centers lying on the straight line representing the central meridian.

15. Azimuthal: Projections in which the meridians are represented by a system of concurrent straight lines inclined to each other at their true difference of longitude, and the parallels by a system of concentric circles with their common center at the point of concurrency of the meridians.

16. C ylindrical projections • Cylindrical equidistant • it is formed bringing a cylinder into contact with the spehe and peeling the meridians off the sphere and onto the cylinder without any distortion. • this maintains scale factor along meridians = 1 • scale factor along parallels: sec φ

17. Cylindrical • meridians are straight and parallel to each other • the distances along the meridians are undistorted • the scale along the equator is true by the scale of all other parallels becomes increasingly distorted towards the poles • sec 90° = infinity • shape and area become increasingly distorted towards the poles

18. Cylindrical • shape and area become increasingly distorted towards the poles • plate carréé - sometimes used name for certain forms of this projection

19. Cylindrical • the first step is to select the origin for the projection • latitude and longitude • Eastings coordinate is calculated as the distance along the equator between the projected point and the origin

20. Cylindrical • True cylindrical projections have these three points in common (in their equatorial cases), • 1. meridians project to straight lines, • 2. parallels project to straight lines, • 3. meridians and parallels cross at right angles.