Verifying the map features
5 Some map features may require additional verification. For example, some streams may run only intermittently, in which case they would be represented on the map by a dash-dot or lighter-weight instead of a solid line. Certain roads may turn out to be private roads, rather than public roads, and these must be marked. Field checkers go into the area and verify these features by talking with local residents or consulting local property records. Any questionable features noted by the survey crews must also be verified. The correct spelling of place names must be determined.
Compiling the map manuscript
6 After the area has been surveyed and all the features have been checked, the pairs of overlapping aerial photographs are placed in a stereoscopic projector. One image is projected to the operator's left eye and the other image to his right eye. The result is a three-dimensional view of the terrain. Two small beams of light are connected to a pointer and are adjusted to intersect in a tiny white dot corresponding to a given elevation on the three-dimensional terrain image. By
To ensure the accuracy of a map, the exact location of various control points must be established by field surveys. A separate scribecoat is made for each color used.
moving the pointer while keeping the two beams focused in a dot, the operator traces each contour line of the ground and the location of various features. The pointer is connected to a pen on the tracing table that draws the contour or feature being traced. All contours and features are drawn in black at this point. This process is called compiling the map manuscript.
7 When the tracing is completed, the finished map manuscript is photographed, and a map-sized film negative is made. This negative is photochemically reproduced onto several thin plastic sheets coated with a soft, translucent coating called a scribecoat.
Scribing and editing the map
8 The plastic sheets are taken one at a time and placed on a light table, where a soft light shines up through a white plastic surface. This illumination from below makes the lines of the map manuscript visible through the scribecoat. An engraver carefully cuts away the scribecoat along the lines and areas that are to be a certain color on the finished map. For example, one sheet will have all the lines for rivers, lakes, and other bodies of water that are to be blue. This process is repeated for each color.
9 Separate sheets for the lettering are prepared by placing a clear plastic sheet over each scribed sheet and carefully aligning the lettering with the features to be labeled. Type sizes, styles, and fonts are selected according to standards, which assure consistency and legibility from one map to another. A film negative is then made of each finished type sheet.
10 After the scribed sheets are reviewed and edited several times, a color proof sheet is made by exposing each sheet under different color light to produce a color print that looks very much like the finished map. After further review and editing, the map is ready to be printed.