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NOAA Datums Videos 2014

Differential correction with NA2011 and the newest epoch of NAD83

See our and Datums Basics and GPS Tutorials for the long-awaited results of months of rigorous testing and peer review

Trimble Positions software has replaced Trimble GPS Analyst in ArcGIS 10.1

ALASKA GPS and GIS users - check out Joel Cusick's Datum and Projections presentation Feb 2013

ArcGIS 10.1 - New and Cool improvements see Presentation from Melita Kennedy, ESRI : Projections and Datums Dec 2012

Home GIS Basics Combining Data of Different Datums
Combining Data of Different Datums PDF Print E-mail

This shift is typical of a datum mismatch.


mixing_datums

The city park features collected by GPS have landed blocks away on rooftops. They have shifted approxiamtely 80 meters east and 200 meters south of where they should be on the background image. This is because while the aerial photo is in the NAD83 datum, the GPS data has been exported to GIS in the NAD27 datum.  For this area, a coordinate in NAD27 is not surprisingly given the above example, 80 meters east and 200 meters south of the same coordinate in NAD83.

To avoid datum shifts

ALWAYS document the datum and coordinate system for all datasets you create and check the metadata for datasets you recieve from others.  Failure to do so is the most common reason for mismatched data.  While GIS software can project on the fly, it needs to know the projection each dataset is in to do so successfully.

Metadata, data about our data is always critical.

Here is a fun (really!) 6-minute METADATA video that uses HUMOR to drive that point home.