Wed Feb 15, 2012 7:20 am
11.3 Supply Distribution
Conceptually, each turn military units and structures draw supplies from other supply producing/storing structures. This distribution of supplies is handled automatically by the computer during the game turn and is not visible to the player (i.e. Supply distribution is handled by supply columns which are not represented by actual units). This abstract handling of supplies is done by computer so as not to burden players with unacceptable levels of micromanagement.
11.3.1 Limitations on Supply Distribution The amount of supply points that can transit a structure during any given game turn is roughly limited to the production capacity of the structure. For example, a level 8 un-besieged city is able to distribute 64 points of General Supply and 16 points of Ammunition (subject to certain modifiers) in a single game turn. Depots, however, have enhanced abilities to distribute supplies (equal to a level 15 city).
11.3.2 Transit Distance for Supply Distribution The maximum distance that supply points may travel from a supply source to a requesting unit or structure is three (3) map regions. However, this distance is affected (i.e. often reduced) by the type of terrain being transited, inclement weather, and the presence of enemy forces. Important:
Supply may only transit through regions in which a player has a minimum of 25% Military Control . (Enemy light cavalry units acting as Raiders automatically block all supply from transiting a region in which they are located.)
11.3.3 Supply distribution by Rail Each turn, the trains left unused during the movement phase (see p.) will be available for Supply distribution. These will be used to transport Supply over friendly rail lines.
Note: Controlling railroads are strategically important, as they allow you to transport great quantities of Supply and men compared to overland Supply paths using roads.
These rules or explanation of supply are the core answer to your query.
You need to look for bottlenecks. I think of bottlenecks as places which are less than 15 movement points or days from point to point. So if you are going from source to desination, each 15 day stretch of rail will be free of these:
A city of less capacity to push supply
Enemy units
Broken rail
Enemy control or your own control of less than 25%.
It will contain high capacity cities or depots at least every 15 mp or days by rail.
All of this equals good supply.