Given that we have digital topgraphy, it is easy to examine a line across the topography and determine what is visible. The following is from demo\topo\profiles&views.mxd
To complete this in a MAP VIEW to make a "viewshed," we need to rotate analysis 360 degrees around a point or each of a series of points or lines. Below is that analysis for a house located at about 990 ft on the profile above.
For multiple locations or lines (like roadways) this analysis becomes significantly more complicated and CPU consuming.
In 2002, this analysis took about 5 minutes on our 1.5 km by 1.5 km grid (50 by 50 grid). (I think there must be an error here, because all the houses are lower than the ridgetop, and yet visibility creep across it to the left (must be a cave tunnel)). Now it takes just a few minutes. What part of visibility have we missed? Can we add any more information?
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