
Azimuthal projection
One type of map projection that retains certain accurate directions. Azimuthal also refers to one type of map projection that uses a plane as the projection surface.

Central lines
The central parallel and the central meridian. Together, they define the center of the origin of a map projection.

Clarke 1866
A groundmeasured spheroid, which is the basis for the North American Datum of 1927(NAD27).

Conformal projection
One type of map projection that preserves local shapes.

Conic projection
One type of map projection that uses a cone as the projection surface.

Cylindrical projection
One type of map projection that uses a cylinder as the projection surface.

Datum
The basis for calculating the geographic coordinates of a location. A spheroid is a required input to the derivation of a datum.

Decimal degrees (DD) system
A measurement system for longitude and latitude values such as 42.5^{o}.

Degreeminutesseconds (DMS) system
A measuring system for longitude and latitude values such as 42^{o}30'00", in which 1 degree equals 60 minutes and 1 minute equals 60 seconds.

Ellipsoid
A model that approximates the Earth. Also called spheroid.

Equidistant projection
One type of map projection that maintains consistency of scale for certain distances.

Equivalent projection
One type of map projection that represents areas in correct relative size.

False easting
A value applied to the origin of a coordinate system to change the xcoordinate readings.

False northing
Avalue applied to the origin of a coordinate system to change the ycoordinate readings.

Geodetic coordinates
Geographic coordinates that are based on a spheroid.

Geographic Coordinate Data Base (GCDB)
A database developed by the U.S Bureau of Land Management (BLM) to include longitude and latitude values and other descriptive information for section corners and monuments recorded in the PLSS.

Geographic coordinate system
A location reference system for spatial features on the Earth's Surface.

GRS80
A satellitedetermined spheroid for the Geodetic Reference System 1980.

Lambert conformal conic projection
A common map projection, which is the basis for the SPC system for many states.

Latitude
The angle north or south of the equatorial plane.

Longitude
The angle east or west from the prime meridian.

Map projection
A systematic arrangement of parallels and meridians on a plane surface.

Meridians
Lines of longitude that measure locations in the EW direction on the geographic coordinate system.

NAD27
North American Datum of 1927, which is based on the GRS80 speroid and has its origin at the center of the spheroid.

Parallels
Lines of latitude that measure locations in the NS direction on the geographic coordinate system.

Principal scale
Same as the scale of the reference globe.

Projected coordinate system
A plane coordinate system that is based on a map projection.

Projection
The process of transforming the spatial relationship of features on the Earth's surface to a flat map.

Public Land Survey System (PLSS)
A land partitioning system used in the United States.

Reference globe
A reduced model of the Earth, from which map projections are made. Also called a nominal or generating globe.

Reprojection
Projection of spatial data from one projected coordinate system to another.

Scale factor
Ratio of the local scale to the scale of the reference globe. The scale factor is 1.0 along a standard line.

Spheroid
A model that approximates the Earth. Also called ellipsoid.

Standard line
Line of tangency between the projection surface and the reference globe. A standard line has no projection distortion and has the same scale as that of the reference globe.

Standard meridian
A standard line that follows a meridian.

Standard parallel
A standard line that follows a parallel.

State Plane Coordinate (SPC) system
A coordinate system developed inthe 1930s to permanently record original land survey monument locations in the United States. Most states have more than one zone based on the SPC27 or SPC83 system.

Transverse Mercator projection
A common map projection, which is the basis for the UTM grid system and the SPC system.

Universal Polar Stereographic (UPS) grid system
A grid system that divides the polar area into a series of 100,000meter squares, similar to the UTM grid system.

Universal Transverse Mercator (UTM) grid system
A coordinate system that divides the Earth's surface between 84^{o} N and 80^{o} S into 60 zones, with each zone further divided into the northern hemisphere and the southern hemisphere.

WGS84
A satellitedetermined speroid for the World Geodetic System 1984.

xshift
A value applied to xcoordinate readings to reduce the number of digits.

yshift
A value applied to ycoordinate readings to reduce the number of digits.

