Comparison - Gavdos Island EVS vs PGS
Gavdos and Gavdopoula Islands - Map
Ever since I began using the Prototype Global Shoreline (PGS) map files in place of World Vector Shoreline (WVS), I find reason to compare it to my Enhanced Vector Shorelines (EVS), which makes up the shorelines of all of my maps.
Gavdos Island - Map (Detail EVS vs. PGS)
The PGS shoreline is the dark blue line and the EVS shoreline tracks the island shape. This map is shown at 1:10,000 scale. At this scale the PGS does not closely track the Landsat shoreline. It is a problem with the parameters of the original mapping algorithm used by EarthSat when they constructed the PGS shoreline. At a scale of 1:125,000 the PGS and EVS appear to track each other with a great deal of precision. It is when you zoom into the finer scales that PGS tracks less and less precisely.
PGS needs to become the ultimate global shoreline map file. It is derived from Landsat 2000 imagery. Consequently, it should track shorelines as consistently and precisely as possible. Although it is close, "no cigar" yet. PGS should track shorelines as consistently and precisely as EVS is able to do. Will it ever?
More about this topic later.
