Hi Martin,
Interesting! I guess the main issue would be wind-direction, but if this isn't being considered in this exercise then your suggestion of using a polygon to represent the 'cloud' would be best. I would make it irregular, rather then just a circle, and make it grey with transparency, so the base mapping can be seen. Here's a couple of examples I've just knocked up using the eclipse tool and then merging objects together.

I guess you could add a symbol to show the point of escape, if that was relevant.
Interesting to see what others come up with.
Greg
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Greg Driver
Knowledge Community Shared Account
Shelton CT
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