Quality Control and Potential Errors 



65. All sections of shoreline from the source maps were digitized so 

 that all shoreline points could be converted into GP's and replotted at any 

 desired scale (before the final portrayal scale of 1:24,000 for the shoreline 

 movement maps was chosen, other scales were tested to determine which map 

 scale would portray the data in the most readable form) . Digitizing also re- 

 moved inherent media distortion caused by the age of the original manuscripts. 

 The mechanics and mathematics of the digitizing system required that all pro- 

 jection (latitude and longitude) intersections completely enclose the data to 

 be digitized. By assigning known and true values for each projection inter- 

 section, the GP0LYT2 program adjusted each of the shoreline points enclosed 

 within a projection cell, based on the true values of the intersections versus 

 the digitized and computed values for those same intersections. The values 

 for each shoreline point are thus correct in their position relative to the 

 known (true) projection intersections and to known triangulation data 

 (Figure 26). 



-k- 



44- 



+ 



DIGITIZED VALUES 



~t~ CORRECTED VALUES 

 ' ADJUSTED TO TRUE 

 VALUES FOR 

 INTERSECTIONS 



Figure 26. Digitization procedure for correcting shoreline position 

 locations when original shoreline movement map distortions exist 



66. Following the digitizing process, each sheet was reviewed visually 

 with the use of a raw data plot in which shoreline positions were shown at the 

 same scale as the original map. The plotted shoreline was superimposed on the 

 original map and checked for completeness and accuracy of tracking during dig- 

 itization. This review helped to minimize a potential source of human error 

 that could occur during the digitizing process. 



52 



