How do I sanity-check the georegistration I made manually with TerraGo Composer?

There are a couple of general techniques. A simple one is to use the Google Map It! feature of the GeoTool to verify that a feature on the map shows up in Google Maps. Another is to check to see if you’re recovering the coordinates marked on the map, e.g., at the intersection of lines of longitude and latitude marked on the map. If you have used more than 3 points to georegister the map, the Georegistration tool will display the mean square error (MSE) associated with the individual points. While the MSE is not an indication of the accuracy of the georegistration, a point with a significantly higher MSE than the others might indicate problem with that point.