Obst lamp
I am not sure that I understand the problem. You say
I come up against a mast which technically isnt high enough to be an issue, but due to its location may be a problem.
So what exactly is the problem - the establishment of a new mast or the unserviceability of the lighting on an existing one? What is wrong with having the set of three paper 1:500,000 aeronautical charts and merely comparing the known lat/long or as derived from Google Earth, and then seeing whether there is a nearby aerodrome. Whether the site is inside or outside an ATZ is not the criterion and I can't help feeling that you might be looking at the issue from a wrong angle by getting involved with other, irrelevant, aeronautical data. Would not your company have on record whether each mast constituted an obstacle and whether it was required to be lit?
2 s