**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.