Module 4 - Ground Truthing & Accuracy Assessment

This week was all about 'ground truthing' classification maps and evaluating the overall accuracy of the classes assigned.  Using the Land Use / Land Cover map created for Module 3 we 'ground truthed' our own classifications.  Overall my map from last week was 67% accurate... ouch!

The above map had been 'ground truthed' for accuracy - overall accuracy was found to be 67%.

Since physically visiting Pascagoula, Mississippi was not an option for me (or most of my classmates) we used Google Maps as our higher grade dataset, then visually compared pre-selected sample locations against Google Maps. 

The sample locations were derived using a stratified random scheme, with at least 2 points per class type.  Most classes had 3 points, and two classes (which did not have very large representation on the map) had only 1 point.  The largest class contained 4 sample points.  Sample locations were plotted using a program called the Sampling Design Tool.  The program is available as a download through ESRI and was created by NOAA's Biogeography Branch.

After checking Google Earth against the sample point locations on my original LULC map, I have some basic observations:

1. My original cropland designation apparently was just grass mowed with a distinctive pattern... I'm still not buying it, and believe instead that the land use has changed over the years.
2. My beach was apparently someone's home - they live right on the water and seem to have little to no landscaping.  That was not readily apparent at my MMU of 1:4,000.
3. I should have set 3 sample points per class, and then manually messed with their location.  Many of the sample points were bunched up for some reason.  Also, classifications that did not cover as much map space should have had at least 1 sample point taken away.  But the largest classes didn't really need to absorb those 'excess' sample points.