ASIS:Data mask

The first image below shows both the 5 km mask provided by Jon Bamber (grey category data) and the ADD (v5) coastline data. There is some disagreement between the two around the Amundsen Sea area. The next two figures show the ADD data overlain on the RAMP and MODIS images, the ADD dataset appears more accurate form these images. Jon suggested to me that the dataset was mainly for display purposes, so i think the mask should be based on the ADD dataset.