Excess production is discarded, unless it can be unloaded into the
producer's occupying units, or distributed to nearby units via
supply lines. Supply lines automatically exist between units that
are close enough (as set by the game), and there is no need for explicit
manipulation. Supply line length depends on the game and the units on
both ends, but is not affected by the intervening terrain. Supply
redistribution does not account for special needs anywhere; it just
tries to utilize production excess. The redistribution method is rather
adhoc; units try to get rid of all their excess supply, and try to take
up supply from other units within supply range. Each direction is
controlled independently, so for instance airplanes can get
automatically refueled from a nearby city, but not from each other. No
unit will transfer all of its supply via supply lines. Normally units
in the same cell can exchange supplies, but some games can disable this
behavior (out-length
< 0), so that explicit transfer using the
give and take commands is always necessary.