The location of the map projection origin on the surface, and the coordinate system units

The LCC requires we specify an upper and lower parallel – 20o & 60o

The LCC requires we specify an upper and lower parallel – 20o & 60o

An ellipsoid – GRS 1980

A central meridian – 96o

A projection origin – Lat. 40o

Locally preserves angles/shape.

Locally preserves angles/shape.

Any two lines on the map follow the same angles as the corresponding original lines on the Earth.

Projected graticule lines always cross at right angles.

Area, distance and azimuths change.

A map is equidistant when the distances between points differs from the distances on Earth by the same scale factor.

A map is equidistant when the distances between points differs from the distances on Earth by the same scale factor.

Equivalent/equal area projections maintain map areas proportional to the same areas of the Earth.

Equivalent/equal area projections maintain map areas proportional to the same areas of the Earth.

Shape and scale distortions increase near points 90o from the central line.

A map projections is a systematic rendering from 3-D to 2-D

A map projections is a systematic rendering from 3-D to 2-D

Datum transformations are from one datum to another, 3-D to 3-D or 2-D to 2-D

Changing from one projection to another may require both.

Mercator- A conformal, cylindrical projection tangent to the equator. Originally created to display accurate compass bearings for sea travel. An additional feature of this projection is that all local shapes are accurate and clearly defined.

Mercator- A conformal, cylindrical projection tangent to the equator. Originally created to display accurate compass bearings for sea travel. An additional feature of this projection is that all local shapes are accurate and clearly defined.

Transverse Mercator - Similar to the Mercator except that the cylinder is tangent along a meridian instead of the equator. The result is a conformal projection that minimizes distortion along a north-south line, but does not maintain true directions.

Lambert Equal Area - An equidistant, conic projection similar to the Lambert Conformal Conic that preserves areas.

Lambert Conformal Conic – A conic, confromal projection typically intersecting parallels of latitude, standard parallels, in the northern hemisphere. This projection is one of the best for middle latitudes because distortion is lowest in the band between the standard parallels. It is similar to the Albers Conic Equal Area projection except that the Lambert Conformal Conic projection portrays shape more accurately than area.

Lambert Conformal Conic – A conic, confromal projection typically intersecting parallels of latitude, standard parallels, in the northern hemisphere. This projection is one of the best for middle latitudes because distortion is lowest in the band between the standard parallels. It is similar to the Albers Conic Equal Area projection except that the Lambert Conformal Conic projection portrays shape more accurately than area.

Albers Equal Area Conic - This conic projection uses two standard parallels to reduce some of the distortion of a projection with one standard parallel. Shape and linear scale distortion are minimized between standard parallels.

Projections specify a two-dimensional coordinate system from a 3-D globe

Projections specify a two-dimensional coordinate system from a 3-D globe

Projections differ by datum – know your parameters

Once map data are projected onto a planar surface, features must be referenced by a planar coordinate system.

Once map data are projected onto a planar surface, features must be referenced by a planar coordinate system.

Coordinates in the GIS are measured from the origin point. However, false eastings and false northingsare frequently used, which effectively offset the origin to a different place on the coordinate plane.

The three most common systems you will encounter in the USA are:

State Plane

Universal Transverse Mercator (UTM)

Public Land Survey System (PLSS) – non-coordinate systems

Uses Lambert conformal conic (LCC) and Transverse Mercator (TM, cylindrical)

Uses Lambert conformal conic (LCC) and Transverse Mercator (TM, cylindrical)