Representing a triangular cross section in the plan view..

[John Lovaas]

Hi all-

I'd like to see how other folks would solve this cartographic problem.

We just finished surveying a sandstone cave. One of the passages had a triangular cross section- widest at the top(maybe 8' wide at the ceiling), with the floor width being around 2'.

Obviously the cross section sketch illustrates the passage well- however, how would I represent it in plan view? The walls are bedrock, and slope smoothly to the floors- no steps or ledges.

I guess I could use the same slope symbol I'm using to illustrate changes in the floor slope, or else I could keep the plan view's wall width at the maximum(the ceiling width), and then use a fill to delineate the floor.

Or maybe I'm overthinking this. ;-)

jl

[Jeff Bartlett]

draw the passage as being 8' wide, use the distance from the low point of the floor to the ceiling to denote the ceiling height, and then put a slope pointing down from each wall to meet in the center.

i threw an example together really quickly. in your case, you'll probably want to draw the slope more continuous than what i've shown. that's the value of cross sections - to tell the bit of the story you can't quite tell with the plan view

ps - on my screen, for some reason the thumbnailed image doesn't show the cross section leader line. oh well, it shows up when you click on it. icky.

[John Lovaas]

Hi Jeff-

Unless someone suggests something else, I will likely use the slope indicator in the fashion you mentioned.

That particular symbol makes me think of a sloping sediment floor, but there's no reason it wouldn't apply to a sloping wall.

Thanks! jl

[George Dasher]

Yea... just use the slope indicators for the floor.

It will show nothing of how the passage is shaped, but then that is the purpose of the cross-section.

[Aaron Addison]

JL-

The primary function of the plan view is to show floor detail. I would use the bedrock symbol and only use the slope symbol sparingly. If the cross sections are in close proximity, that should tell the map reader the whole story.

Happy Holidays-

Aaron

[wyandottecaver]

If you showed the passage width at shoulder or mid passage height and put a width line in the cross section you would have less clutter and represent it clearly enough I think.

[robcountess]

I would recommend solving the problem by digging/microblasting the passage until it has a rectangular cross section

[Jeff Bartlett]

If you showed the passage width at shoulder or mid passage height and put a width line in the cross section you would have less clutter and represent it clearly enough I think.

Actually, I think this is technically incorrect; I've been taught that you always show the represent the plan view as it would appear from directly above, which means you always show the passage at its widest. To deviate from this would likely confuse the map viewer more than anything.

However, those who have been surveying (or teaching surveyors) longer than I have can probably clarify this a bit. PK, can we get a ruling here?