proper symbolization. These maps were then digitized, checked, and reviewed 

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



Data Reduction Procedures 



62. Copies of all historical maps used as source data in this study 

 were obtained from the NOS vault in Riverdale, Maryland, through the NOS Re- 

 production Division. Copies were initially bromide prints (a photographic 

 process which provides a long shelf-life copy) and were later made into more 

 stable matte-finish film positives. Historical sheets covering the study area 

 were examined to determine which sections of shoreline would be included in 

 the study, and those were highlighted using a yellow felt marker. Only those 

 areas and sections of shoreline for which data from other NOS historical maps 

 would be available for comparison were used. 



63. Digitizing of the shoreline on each historical map and each base 

 map, revised for contemporary shoreline, was the next task. This procedure 

 was completed by the Data Translation Branch, Environmental Data and Informa- 

 tion Service, Asheville, North Carolina. The digitizing was completed on a 

 Calma-graphics III system, with a repeatability factor of ±0.001 in. and a 

 maximum absolute error of ±0.003 in. The digitized data tapes were then pro- 

 cessed using a program developed by the NOS Marine Data Systems Project for 

 use with the N0AA UNIVAC computer (GP0LYT2) ; this program allows for the con- 

 versions of the 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 (NA 1927) was established, the GP's for these sheets 

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

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

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

 program also written by the NOS Marine Data Systems Project. 



64. After processing of the data was completed, plot tapes were gen- 

 erated using the NOS McGraphics program, and the 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. 



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