HANDRAILS
Handrails are linear features, like roads, power lines, tree lines, fences ,walls,
ridge lines or rivers and streams. They are all features that can run roughly or parallel to your direction of travel,
as long as it travels with you on either the left or right of your intended route. Acting as a handrail to guide the way.
COLLECTING FEATURES
When you reach the point where your route or handrail changes direction, you must be aware that it
is time to go your seperate ways. Some prominent feature located near this point is selected to provide warning. This is called
a collecting feature, it can also be used to tell you when you have gone to far.
INTERVISIBILITY
The subject of intervisibility is concerned with answering questions of the type - is it possible
to see from A to B, or what does A looks like from B, and extensions of such questions as what else can be seen from A or
B.
Looking at the terrain profile below, it is at once evident that A and C are intervisible
B and D are intervisible and C and D are intervisible but A and B and B and C and A and D are not intervisible.
