contract and thereby apply the best methods available. Fully analytical aerotriangulation is currently the most advanced method for extending control for mapping, both horizontal and vertical. Except for identifying and establishing a minimum of field control, all operations can be completed within the office, measuring coordinates on photographs with a comparator (fig. 13) and preparing the data for computer analysis. This method, which the celebrated Otto von Gruber considered merely an academic exercise in the 1930's, has become practical and cost effective with the development of large computers. Today even small firms can use computer services on FIGURE 13.-Wild STK stereocomparator, used for accurate coordinate measurement for analytical aerotriangulation. MAP COMPILATION After aerotriangulation, the map manuscripts are compiled. In compilation, mapworthy details are transferred from source materials to a specially prepared dimensionally stable manuscript base. Lines and symbols portray the details on conventional maps and charts. Orthophotomaps are compiled from rectified photographs, with selected features enhanced by symbols. On topographic maps, relief is portrayed by contour lines. Features must be generalized on maps because the manuscript area is very small in relation to the ground area. Selection of features requires a knowledge of photogrammetry, the ability to interpret images correctly, and the ability to draw lines and symbols accurately. Dimensional stability and suitability of the drawing surface are important factors in selecting a medium for map manuscripts, now generally polyester sheets with a suitable coating. Variations in temperature and humidity little affect polyester bases, eliminating serious cartographic problems. Manuscript preparation begins with drawing the geographic graticule on the selected map projection and the grid lines for a plane coordinate system. Today, this operation is usually automated to the extent of using a coordinatograph, or x, y plotter. Control data are plotted at the same time. The manuscript may be compiled in ink or pencil. Map manuscripts are also compiled on stereoscopic plotting instruments from diapositives, positive transparent prints on glass plates or film. The instruments range from relatively simple types to complex plotters. Some complex plotters are being incorporated into automated mapping systems. When properly used, all are efficient and capable of producing maps that meet accuracy standards. In a stereoplotter two overlapping images are viewed simultaneously to provide a three-dimensional model. The stereoscopic effect is produced when the operator views the same ground area on two perspective photos, one with each eye, at the same time (fig. 14). The different perspective views result from the progressive movement of the aircraft between exposure stations. Although stereocompilers can interpret much of the map detail from the stereomodel, they need help in interpreting some features and in distinguishing between others. Questions always arise, and regardless of how expert the compiler may be, errors in interpretation can occur. In addition, changes in features, especially cultural features, may have occurred since photography. Field classification usually is an annotation directly on the aerial photograph or the photoindex. Annotations include (1) classification of buildings, (2) classification of roads and trails, (3) delineation of boundaries, (4) identification of cultural features, (5) location and labeling of control stations, (6) delineation of streams and classification as intermittent or perennial, (7) delineation of wetlands, (8) delineation of U.S. land lines and labeling of townships and sections, (9) classification of sample woodland areas, and (10) identification of names. Classification and various elements of map completion may occur after compilation of the map manuscript. However, these surveys are generally limited to specific problems and questions, not a general review of the compiled map, so that time and money are always saved by completing the classification in advance along with the control. Stereoplotters are equipped with a reference mark in the field of view that can be moved in three dimensions by the operator. As the reference mark is moved in contact with the apparent surface of the stereomodel, a drawing pencil automatically traces the horizontal motions on the base sheet. Contours are drawn by moving the reference mark along the surface of the model at a preset elevation. Planimetric features are compiled first, directly on the base sheet. Other features, such as woodland and contours, usually are compiled on separate manuscripts. Drainage may be compiled with either culture or contours. The features compiled directly on the base sheet are usually scribed stereomodel by stereomodel. Then, the data are photoprinted onto successive manuscript sheets to guide the compilation of other features. Each manuscript is reviewed after compilation to assure compliance with established specifications and standards. Corrections are made after review. Compilers record all difficulties encountered during compilation. Sometimes they cannot positively identify the image of an object. Sometimes structures are only partially complete at the time of photography. All problem areas are noted on the copy of the manuscript that is sent to the field for final inspection. Photogrammetric techniques can be used to acquire data vital to coastal management aside from production of maps and charts. For example, offshore activities such as structure location; pipeline and cable routing; aquaculture and mariculture design, location, and operation; and recovery of living and nonliving marine resources require a knowledge of water circulation patterns. Lagrangian current measurements obtained by a photogrammetric circulatory survey made concurrently with and in support of a Eulerian current survey provides an enormous quantity of data at reasonable cost. Acquisition of the same data by Eulerian methods exclusively would be prohibitively expensive and, because of equipment limitations, impossible in shallow water. The photogrammetric data can be processed rapidly for presentation in tabular form or in chart format. FIELD COMPLETION As previously noted, efficient production combines all field surveys into a single pass through the area to the extent possible, before the map is actually compiled. If the combined operation is not possible, field completion or field editing surveys remove deficiencies and resolve discrepancies noted during compilation. The mapped features are carefully and methodically compared with ground detail, and horizontal and vertical accuracy tests are applied as required. The field editor certifies that the map is correct and complete. After the additions are completed and verified in the office, the manuscript is ready for final drafting and review, and copies can be made for limited distribution and use. FINAL DRAFTING AND REVIEW Most maps are produced from either scribed or inked drawings. Scribing and inking differ in several ways. Inking forms a positive image and is rightreading; scribing forms a negative image and is normally wrong-reading (right and left reversed) so that positive contact prints are right-reading (fig. 15). In inking, the features to be shown in a specific color are drawn in black ink on a nonphotographic blue guide image of the map detail. In scribing, plastic sheets coated with photographically opaque paint are overprinted with the guide image, and the lines and symbols are cut into the coating with engraving tools (see fig. 16). Corrections can easily be made by covering mistakes with opaquing fluid and rescribing. The effect of scribing can also be obtained photomechanically. The scribecoated sheet is photosensitized and contact-printed with a line drawing or film positive. After exposure, the sheet is developed with an etching solution to remove the opaque coat |