Common Spatial Reference Systems

Common Datums

The most commonly used datums in the US are:

• NAD 83
• NAD 27
• WGS 84

Common Projection Systems

The most commonly used projection systems are:

• Universal Transverse Mercator (UTM)
• State Plane
• Lambert Conformal Conic: For the entire continental US (CONUS) or North America
• Alber's Equal Area: For the entire continental US (CONUS) or North America
• Geographic: For distributing data internationally

Common Spatial References for Northern California

Combining the datums above with units of "US Feet" and meters, gives us the following commonly used spatial references for Northern California.

• NAD 27, State Plane California Zone I, US Feet: This was once the most common and is still used heavily by US agencies and some corporations.
• NAD 83, State Plane California Zone I, Meters
• WGS 84, UTM Zone 10 North (UTM is always in meters): This is the current recommended spatial reference for our area.

Note that other regions will be using different spatial references based on where they are located, the size of their region, and their history.

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