The Game Master will normally place opponents in known encounter areas. Optionally (or for random encounters), the Game Master can determine distance and positions randomly.
If not surprised and no other modifier exists, distance will be 1d6+4 x 10 feet between the two groups.
Modifiers for Surprise. If surprise exists for any party, the distance will be 1d3 x 10 feet. (i.e. d3, 1=melee range; 2=10-20-ft.; 3=21-30-ft.)
Modifiers for Line of Sight. If line of sight exists, there is no modifier. Otherwise, modify distance by line of sight obstructions.
Modifiers for Noise. If one party is making noise, the other may not be surprised, and can avoid the encounter by fleeing or hiding. If hiding, the encounter distance will be 1d4 x 10 feet. Certain types of armor will make considerable noise (see Equipment, Armor).
Modifiers for Size of Encounter Area. Encounter distance must be modified so the maximum distance is equal to the size of the area. Example. In a room 20-ft. by 20-ft., the distance between the two parties can be under 10-ft., 10-ft. or thereabouts, or 20-ft. (d6, 1-2 = melee range, 3-4 = 10-ft. away, 5-6 = 20-ft. away)
Modifiers for Light. Maximum encounter distance will be twice the light radius. Otherwise if infravision or ultravision is possessed by one of the parties, encounter distance will be limited by that range.
If not surprised, base distance is 18d4 x 10 feet between the two groups.
Modifiers for Surprise. Subtract (the larger number of surprise segments × 30 feet) from the distance to a minimum of 10 feet. If all opponents are surprised and there is enough time (in segments) for the surpriser(s) to move (flee) beyond the sight and hearing of the surprised group (and they elect to do this), the surprised group will be unaware of the surpriser(s). See Fast Actions, B. Flee, Avoid Encounter.
Modifiers for Scrub Terrain. Distance modifier is -1 per die rolled above on all 3’s and 4’s.
Modifiers for Forest Terrain. Distance modifier is -1 per die on all numbers (0’s are possible)
Modifiers for Marsh Terrain. Distance modifier is -1 per die on all 2’s, 3’s, and 4’s
Modifiers for Other Terrain. Plains, desert, hills, and mountains do not alter encounter distance variables unless one of the three modifying types of terrain also exists.