Area
The actual area of a shape, in the units of measurement of the map.
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
• the oblique aspect which is tangent anywhere else
Azimuth
The angle, measured in degrees, between a base line radiating from a centre point and another line radiating from the same point. Normally, the base line points north, and degrees are measured clockwise from the base line.
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.
Developable surface
A developable surface is a simple geometric form capable of being flattened without stretching. Many map projects can then be grouped by a particular developable surface: cylinder, cone, or plane.
Direction
The angle between two points (azimuth, bearing, etc.).
Distance
The actual distance between two points, in the units of measurement of the map.
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.
Equidistant
Equidistant maps show true distances only from the centre of the projection or along a special set of lines. No flat map can be both equidistant and equal area.
Graticule
The graticule is the spherical coordinate system based on lines of latitude and longitude.
Great circle
A circle formed on the surface of a sphere by a plane that passes through the centre 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.
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.
Map projection
A map projection is a systematic representation of a round body such as the Earth on a flat (plane) surface. Each map projection has specific properties that make it useful for specific purposes.
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 shorter distance between points unless the points are on the equator or on the same meridian.
Shape
A geometrical figure on a map.
(United States Geological Survey, n.d.)