What is positional accuracy assessment?

Positional accuracy is the quantifiable value that represents the positional difference between two geospatial layers or between a geospatial layer and reality. An example of this is the comparison of the location of roads in a feature class versus their location in a TIFF image. If the feature class and the TIFF are using the same projection, you can assess the positional difference between the feature class and the TIFF. The Positional Accuracy Assessment tool (PAAT) allows you to compare two items to assess a data layer's accuracy in relation to a reference layer of known or unknown accuracy.

To assess positional accuracy, two layers are required: the layer whose accuracy you want to evaluate and another layer that can be used as a point of reference. The uncertainty is defined as the circular error (CE) for two-dimensional features and linear error (LE) for three-dimensional features. The confidence level for the feature class or raster being evaluated can be at the 90, 95, or 99 percent level when you use the PAAT.

You can use z-enabled data for one or both of the layers in a PAAT session. The only time the PAAT will use the 3D component of z-enabled data is when you are comparing a DEM or TIN to a 3D point feature class or shapefile.

The PAAT workflow

Depending on the layers you are using for evaluation and reference, respectively, the workflow below might not be followed exclusively:

• Configure the session.
• Add points.
• Review and save results.
• End the session.