Geography Reference
In-Depth Information
Figure 4. 3D scene of same area using Arcview 3.2 (L.C. Hazell).
In the background errors noted in the text due to contour crossovers in digitising can
be seen. These did not affect analyses.
The slope gradient and 3D model tools produced analyses and
representations with visible errors formed through contour crossing or
incorrect digitising. This occurred with the earlier version of Arcview 3.2;
however, when digitising contours using ARCMap 10, it was necessary to
zoom in or deactivate the Snapping tool to avoid crossing contours or incorrect
joining of different elevation contours. The same technique applies when
editing vertices. This problem occurred only when contours were close to
together.
In spite of this problem, only a small percentage of the final map area was
affected and usually these contour crossings only occurred when contours
were very close together indicating a steep gradient. This would automatically
exclude these parts of the resulting terrain surface from consideration as a
transport route because of the excessive gradients involved. Attempting to
control a twenty tonne stone on steep downward slopes would have been
impractical as replication and historical observation illustrated (Dillon, 2004,
Heyerdahl, 1958, Richards and Whitby, 1997). In any case the analyses
identified safer, more practical options that were nearby (Figure 5).
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