Projected Coordinate System (PCS)

To properly georeference projected data, any PCS must contain:

• Geographic Coordinate System (GCS)
• Projection Method
• Projection Settings
• Linear Units

The most common form of a PCS is a "PRJ" file that accompanies shapefiles and many other file types. If you are curious, open one of these files and you'll either see a GCS or a PCS.

Projection Methods

The projection method varies with the projection system and is selected based on the area the PCS is for. The previous lesson listed some of the most common methods: Mercator, Alber's Equal Area, Lamber Conformal Conic, etc.

Projection Parameters

The parameters vary with the method and set the location and other settings for the projection method.

Examples include:

• Latitude of Origin
• Longitude of Origin
• False Easting
• False Northing
  

Linear Units

Since projections are rectangular coordinates (rather than spherical), they must be in linear units.

• The most common are:
  • Meters
  • Kilometers
  • International Feet
  • US Feet
  • Nautical Miles (for marine data)

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