If the user chooses to shade by survey, each survey will be assigned a different shade color. Unfortunately, overlap in survey coverage sometimes makes the first survey plotted disappear under surveys plotted later. In spite of this problem, total coverage is easy to see. If the user chooses to shade by date, the most recently covered fields are assigned red shades and earlier fields are assigned blue shades. Up to 28 shades are used, one for each day.
All surveys use the same set of shades and dates.
Covered regions older than 28 days are assigned pure blue. This shading technique is useful for finding regions that have not been covered recently and could be usefully searched again. The legend indicates only three dates. This is a bug and should be modified so all dates have a unique color identified in the legend. Here the user can select all surveys or a single survey to examine.