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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 Consider the Scale of Your Data
Consider the Scale of Your Data PDF Print E-mail

When displaying and combining spatial datasets, consider

1) the scale for which each dataset is valid, and

2) the scale of the map product you are viewing.

In this example, the road  data isn't wrong in itself but rather it is being used well beyond its intended scale as well as the scale of the NAIP image (National Agricultural Imagery Program).  This is similar to zooming into a digital photo beyond its intended resolution and revealing only pixilated blocks.

Dataset                              Scale              Accuracy

GIS Road data                  1:100,000     50.8 meters

Background image            1:3,780              5 meters

Map display                        1:3,780              5 meters

Consider scale when displaying any data and combining differing datasets.

For example, when collecting a particular trail amidst desolate rural miles, 'close enough' with a recreational grade GPS is sufficient for navigation. Yet, how will that same data appear when displayed atop imagery that is accurate down to 5 meters?

...now that we've covered scale, what about datums and coordinate system?