Snap and query buttons are enable only after the user points and snapped points are respectively available. The buttons are disable when snap or query are taking place and are enable again after processing is completed.
Clicking repeatedly snap button do not cause error.
At least one check box selected otherwise an error modal dialogue appears (based on Merret code).
Progress bar bellow snap button changed to "Processing..." to be consistent with query buttons.
Download ZIP button now appears after at least one output (i.e. data frame with snapped points) is produced.