corrected to true latitude and longitude positions as previously discussed. 

 The GP0LYT2 program printout provided a final error column each for "Latitude 

 Y" and "Longitude X," which were examined on each printout. In the event any 

 errors exceeded 0.5 mm (at map scale), the digitizing effort was rejected, and 

 the original sheet was redigitized. Maximum allowable error from this source 

 was 4.99 m on the ground for a 1: 10,000-scale map and 9.99 m on the ground for 

 a 1: 20, 000 -scale map. However, rarely were error column values as high as 

 0.5 mm; in most cases, they were 0.2 mm or smaller. Possible errors from this 

 source were more likely to be on the order of 1.99 m on the ground for a 

 1: 10,000-scale map and 3.99 m on the ground for a 1 : 20,000-scale map. Since 

 most data were finally portrayed at a scale smaller than maps being digitized, 

 the shoreline movement maps produced are well within map accuracy standards. 

 Table 3 is a listing of the GP's of each base map used in this study. 



Data Analysis 



61. Data for this shoreline analysis report were obtained by digitizing 

 shoreline positions on 30 of the 32 base maps produced by NOS (Figure 18) . 

 Maps 12 and 19 did not contain any information on oceanic shoreline changes. 

 Shorelines were digitized from individual mylar copies of each survey since 

 composite mylars were unavailable and paper is an unsuitable medium for accu- 

 rate results because of shrinkage and expansion. Digitizing is the process by 

 which map data are transformed into a digital format. In the case of shore- 

 line analysis, coordinate pairs are assigned to shoreline locations relative 

 to some arbitrary axis system. Data pairs were compared by employing various 

 numerical techniques to produce estimates of mean shoreline movements, vari- 

 ations in the rate and direction of movements, and maximum net movements. 



62. The entire coastline for this report was divided into segments 

 based on general orientation and natural breaks in shoreline continuity, i.e. 

 inlets (Figure 20) . Baselines were chosen for each segment to lie as parallel 

 as possible with the natural trends of the shoreline. Start and end points 

 were located on the composite paper copies midway between the most landward 

 and seaward shorelines. Baseline end points were superimposed onto the indi- 

 vidual mylar copies to define the baseline for each segment for each map. A 

 standard Cartesian coordinate system was then assigned to each segment with 

 the positive x-axis directed generally north to south and the positive y-axis 



46 



