What Contours Don’t Say!
How A Bad Assumption
Can Break Your Neck!
They Don’t Say A Lot!
• We cannot assume anything about the
rate of change between contours.
• Positions within a contour cannot be used
to wisely interpolate between contours
• Minor contours need to be added when
rate of change needs to be demonstrated.
Two paths from 13,200 to 13,600
• The two red arrows are paths with the same vertical
change of about 400 feet. The shorter arrow is a much
steeper approach to the summit than the longer one.
• The change in elevation within the red box is much more
severe than along either of the red arrow paths. It is a
near vertical face. If you tumbled down that slope, a
broken neck might be the least of your problems!
Descent into Oak Creek Canyon, AZ
• The two red arrows are across the same span in the map and satellite photo.
The span covers about 400 meters horizontally with a descent from about
1800 meters to about 900 meters.
• The blue arrow is a similar horizontal span, but the only thing we can say
about the change in elevation is that it is less than 200 meters since we stay
within the same contour. From experience, it has lots of neat curves, but is
almost flat.
A Path Description
Describe the path ABCDA
B
A
D
I made an incredibly steep
ascent then continued up a
gentler slope to a saddle at
about 13,600 feet.
I then made an increasingly
C steeper ascent to the summit
at C (14,410 feet)!
I return to the start point with
an almost linear change in
elevation until I reached D
where I stumbled and fell
down a very steep face to my
start point.