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planimetrically correct, orthophotos can be used as maps for making direct measurements of distances, angles, positions, and areas without making corrections for image displacements (Wolf, 1974). A shortcoming of orthophotos should be noted: relief displacements of extreme vertical surfaces cannot be removed with differential rectification. In most cases, this occurrence is irrelevant to the GCES work because the mapped area does not extend beyond the top of the old high water zone. Once the drafting is complete, the mylar overlays are quality checked by cross-referencing them with the CIR photos and the classification templates. The data are then scan digitized into digital format. Scanning The hardware used in the scanning process is a Tektronix 4991 autovectorizing scanner connected to a UNIX-based Tektronix model 4325 graphics workstation. The software used in scanning is Tekscan (Tektronix scanning software). Tekscan controls all scanning operations and converts scanned data from the original raster format to (IGES) International Graphics Exchange Standard, a format compatible with ARCANFO. The drafted mylar overlays are then tested for the scanning parameter values that produce the most accurate vector product and minimize the editing procedure. A series of scans is performed on a small representative area of a mylar overlay. Once the scanning parameters are established, the hard copy overlays are converted into digital IGES format. The IGES data are converted to ARCANFO coverages by using the ARCANFO IGESARC function. At this point, the data are a series of ARC/INFO master coverages in digitizer inches representing all the aforementioned classes. Editing Line errors detected in the master coverages are usually caused by failure of the scanner to pick up the data drafted on the mylar. These errors are caused by inconsistent line work by the draft person and limitations within the scanner. Line errors in the master coverages are identified using an ARCEDIT function that highlights overshoots (lines that go beyond intersections) and undershoots (gaps) within the line work. Corrections to errors are made by registering the original drafted mylar to a digitizing tablet, hand digitizing missing line work, and deleting the overshoots. The scanned and edited master coverage is then transformed from digitizer inches to Arizona State Plane Coordinate System, generating a RMS (Root Mean Square) of no greater than 0.3 meter. An RMS error of 0.3 meter falls well within the 2.03-meter limit required by National Map Accuracy Standards at a scale of 1:2,400. After the editing process has been 17