terrain attributes within a thematic layer must support or coincide with 
attributes in other thematic layers. 
Data Compilation 
Initially, the compiled terrain data base will consist of six themes or 
layers of information. To date, the land cover, road network, and sur- 
face drainage layers have been compiled (Figure 1). These three files 
contain more than four megabytes of data (Table 1). 
File Name Size in kbytes Compilation Time in Man-Hours 
Road Network 352 64 
Surface Drainage 524 80 
Land Cover 3,185 108 
DEM 5,784 TBD 
Soils TBD TBD 
Landforms TBD TBD 
* TBD: To be determined 
TABLE 1. Information on terrain data base files. 
Soils and landforms, as well as elevation data with a 5 meter resolu- 
tion, are presently being compiled. Data on obstacles, control points, 
and mobility will be added later. 
The requirement for high accuracy weighed heavily in deciding what data 
sources should be selected for use in data capture. As a result, aerial 
photographs were the only source considered. The basic concerns in 
selection of photography were large scale, recent date, and image qual- 
ity. Immediate availability of imagery and camera calibration data also 
were considered. Photos used for digitizing were stereo black and 
white, dated 9-29-76, at a scale of 1:12,000. At this scale eleven 
stereo models cover the test site. Also acquired were stereo natural 
color photography dated 7-8-78, at a scale of 1:28,000, and color 
infrared photos, dated 10-5-83, at a scale of 1:58,000. These photos 
are used for updating information in areas where changes may have taken 
place. 
The CAPIR system employs the use of a GIS and a photogrammetric analyti- 
cal plotter equipped with stereo superposition displays for data cap- 
ture. The spatial data are in an arc/node format with left-center-right 
type attribute entry when digitizing. In addition to digitizing, the 
GIS also provides for aerotriangulation, editing, topological verifica- 
tion, and data base operations. 
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