Azimuthal Projection: A map projection that preserves directions (azimuths) from one or two points to all other points on the map.
Cartesian Coordinate System: A coordinate grid formed by putting together two measurement scales, one horizontal (x) and one vertical (y).
Conformal Projection: A map projection that preserve shape by sacrificing the fidelity of sizes.
Conic Projection: A map projection that yields straight meridians that converge toward a single point at the poles; parallels that form concentric arcs.
Coordinates: A set of two or more numbers specifying the position of a point, line, or other geometric figure in relation to some reference system.
Cylindric Projection: A map projection where projected graticules are straight meridians and parallels that intersect at right angles.
Decimal Degrees: The expression of geographic coordinates in the decimal form (i.e., 43.0753°).
Degrees, Minutes, and Seconds: The expression of geographic coordinates by degree, minute, and second values (i.e., 89° 24' 2" S).
Distortion Ellipse: A tool to visualize what type of distortion a map projection has caused, how much distortion occurred, and where it occurred.
Ellipsoid: A three-dimensional geometric figure that resembles a sphere, but whose equatorial axis (a) is slightly longer than its polar axis (b).
Equal-Area Projection: A map projection maintaining correct proportions in the sizes of areas on the globe and corresponding areas on the projected grid (allowing for differences in scale).
Equator: The equator is the 0-degree line of latitude.
Equidistant Projection: A map projection that allows distances to be measured accurately along straight lines radiating from one or two points only.
Geodesy: Geodesy is the scientific study of Earth’s size, shape, and gravitational and magnetic fields.
Geographic Coordinate System: The coordinate system that is used to specify positions on the Earth's roughly spherical surface.
Geoid: The equipotential surface of the Earth's gravity field; put simply, it has the shape of a lumpy, slightly squashed ball.
Gnomonic Projection: A map projection displaying all great circles as straight lines.
Graphic Scales: A visual tool for representing map scale; unlike representative fractions, graphic scales remain true when maps are shrunk or magnified.
Graticule: The graticule is the geographic coordinate system’s grid.
Great Circle: The most direct path between two locations across the surface of the globe.
Horizontal Datum: An abstraction which defines the relationship between coordinate systems and the Earth's shape.
International Date Line: Roughly the +/- 180 line of longitude.
Lambert Conic Conformal: A map projection whose parameters (such as standard line(s) and central meridians) are optimized for each particular zone.
Latitude: The east-west scale of the geographic coordinate system.
Longitude: The north-south scale of the geographic coordinate system.
Map Projections: Systematic transformations of the world (or parts of it) to flat maps .
Map Scale: The proportion between a distance on a map and a corresponding distance on the ground (Dm / Dg).
Meridian: A line of longitude.
Nominal Scale: A map scale line at which deformation is minimal.
Origin: The point at which both x and y equal zero.
Parallel: A line of latitude.
Planar Projection: Map projection (also called azimuthal projection) that yields meridians that are straight and convergent, and parallels form concentric circles.
Plane Coordinate System: A coordinate system defining a location on the Earth using x and y coordinates.
Prime Meridian: The line of longitude defined by international treaty as 0°.
Project: A method of representing the surface of a sphere or other three-dimensional body on a plane.
Pseudocylindric Projection: A variation of cylindric projection in which meridians are curved.
Representative Fraction: Proportion between a distance on a map and a corresponding distance on the ground (Dm / Dg) in which map distance (Dm) is always reduced to 1 and is unit-less.
Scale a Map: to reproduce a map at a different size.
Scale Factor at Central Meridian: the ratio of map scale along the central meridian and the scale at a standard meridian, where scale distortion is zero.
Standard Lines: A line specified in spatial reference information of a projection along which there is no scale distortion.
State Plane Coordinates: (SPCs) A plane coordinate system consisting of a set of 124 geographic zones or coordinate systems designed for specific regions of the United States.
Transverse Mercator: A map projection that is an adaptation of the standard Mercator projection.
Unit-less: A value that has no units attached, it has the same meaning if we are measuring on the map in inches, centimeters, or any other unit.
Universal Transverse Mercator Coordinate System (UTM): A coordinate system which divides the remainder of the Earth's surface into 60 zones, each spanning 6° of longitude.
Unprojected: Coordinates which have not yet been projected to 2-D surface.
Variable Scale: A graphic representation of scale that shows variability of scale across a map.
Vertical Datum: A reference surface, such as mean sea level.