>>>I'm standing outside. I would have to guess at the height of the clouds, but is there a basic calculation to tell me how far away, by land, that cloud is? Is it simply a2 + b2 = c2? Not counting for the curvature of the earth? I think kind of yes, but since I'm only guessing at the height of the cloud (a2), and I don't know the distance on land from where I'm standing to directly underneath the cloud (b2) and I sure don't know the distance I am fro the cloud directly (c2) then I must have to use angles. This all came about because a little girl asked me how far away a cloud was. What was it over?
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>>I'd have thought they were very close to you, as in standing on one in Cloud Cuckoo Land!
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>>Get yourself a theodolyte then run around the countryside measuring angles to the same cloud, hoping it hasn't moved while you were racing, then you can use trig.
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>Was hoping for something a bit more rudimentary. If the cloud is roughly 30 degrees from me to the horizon, and I guss that it's 1,000 feet in the air, etc. Just looking for something rough. Is it over the next block or is it over the next city?

So you have a rectangular triangle, with the altitude being one side, and the line from your eye being the hypotenuse. Hence,

distance*sin(30)=1000

Which can be solved with calculator.exe (pull up the scientific version)... or you may remember that sin(30)=0.5, ergo the cloud is 2000 ft from you.