not enough features to assure proper positioning, stereo models were set on 

 the National Ocean Survey Analytical Plotter (NOSAP) . The NOSAP is a high- 

 precision stereoscopic plotter that allows the operator to bridge over areas 

 of sparse control and accurately determine correct relationships between pho- 

 tographic models and base maps. Because of time restraints, no field check of 

 the office-determined MHWL was made. All shorelines compiled by this method 

 were reviewed to assure a uniformity of photo- interpreted shoreline, accuracy 

 of compilation, and proper symbolization. These maps were then checked and 

 reviewed in the manner identical to that used for all historical source maps. 



53. Digitizing of the shoreline on each historical map, and contempo- 

 rary shoreline base maps, was then completed by the Data Translation Branch, 

 Environmental Data and Information Service, Asheville , NC. Digitizing was 

 completed on a Calma-Graphics III system, with a repeatability factor of 

 ±0.025 mm and a maximum absolute error of ±0.076 mm. Digitized data tapes 

 were processed using a program developed by the NOS Marine Data Systems Proj - 

 ect for use with the NOAA UNIVAC computer (GP0LYT2) ; this program allows for 

 conversion of digitized data to geographic positions (GP's). Since many of 

 the historic sheets used in the study were completed before the North American 

 Horizontal Datum of 1927 (NA1927) was established, GP's for these sheets were 

 converted to that datum so that accurate comparisons between pre-NA and 

 post-NA 1927 surveys could be made. Conversion was completed mathematically, 

 based on conversion factors for triangulation stations in the area, with a 

 program written by the NOS Marine Data Systems Project. 



54. After processing of data was completed, plot tapes were generated 

 using the NOS McGraphics program. Plot tapes were used with a Calcomp 748 

 plotter and Calcomp 925 Controller to plot the shoreline movement maps. This 

 task was completed with the assistance of the NOS Automated Cartography Group. 



55. 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 

 removed inherent media distortion caused by the age of the original manu- 

 scripts. Mechanics and mathematics of the digitizing system required that all 

 projection (latitude and longitude) intersections completely enclose the data 

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



43 



