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John D Salt

I play Crossfire in the N Mediterranean theater! It’s very interesting to see a game where most of the battlefield is defined by crest lines and depressions, instead of buildings and woods. I use 6mm so that I can have contours actually block the figure’s line-of-sight, it gives you a whole new appreciation for how terrain affects visibility.

Now that’s an interesting observation. Since the effectiveness of modern weapons is more often limited by intervisibility than by mere distance, having a good model of the terrain in pretty important anyway, but in the case of “Crossfire” it also largely does away with any objections to the simplification of not bothering to measure range.

I don’t know how precisely you delineate crest lines — naturalistic terrain models make them a bit hard to nail down exactly — but there is a mathematical formalism (going back to the mid 19th century, see https://www.ucl.ac.uk/bartlett/casa/sites/bartlett/files/migrated-files/paper43_0.pdf ) that describes a landform very simply using summits, immits (low points), saddle points, crest lines and course lines. If you imagine draining water from a flooded landscape, the summits (local maxima) are the first points to appear as the eater is drained, and the immits (local minima) the last. Crest lines connect summits to summits; course lines connect immits to immits; and saddle points are where a crest line and a course line cross (the point is a local maximum in some cross-sections, a local minimum in others). This sort of representation makes if fairly obvious what the field of view (viewshed) from any point to the local horizon. I suspect that Coutney Allen did an analysis along these lines to help him define the areas in his area-movement game “Thunder at Cassino”.

A similar approach used to be recommended to junior officers as part of their terrain appreciations, using the mnemonic GROUND:

G — General
R — Ridges
O — Observation
U — Undergrowth
N — Non-passable
D — Defilade

Under “Ridges”, Infantry Training Part VIII says:

“Take a grease pencil (any other colour except blue) and mark on a talc with a single line the highest part of all ridges and spurs (i.e., the watersheds). Mark the streams or lowest lines of valleys and re-entrants in blue (i.e., the water-courses).”

All the best,