I've had my coffee now and I see the geometry this way: The "essential area" is the area between two horizontal levels of scaffolding (say 2 meters apart). Five measurements are made at 1-meter intervals along a horizontal line at knee level; and five more at 1-meter intervals along a horizontal line at shoulder level. The result is the "local coating thickness" for this area -- which measures say 2 meters vertically (scaffold to scaffold level) and 6 meters horizontally (5 meters between measuring points plus one half meter at each end, where the adjacent "local area" begins, in which the next such measurement is defined) and so on, conceivably around the oil rig structure (or whichever part of it). Presumably the values for all "local areas" are recorded, e.g. perhaps mapped on a geometric diagram of the structure. -- Ask again after I've had my Southern Comfort nightcap, and maybe I can see this all more clearly.