Wilderness Random Encounter Distance

Wilderness Random Encounter Distance

When a random encounter happens, be it in a dungeon or wilderness, how far apart are the party and the monsters? GURPS Dungeon Fantasy 16: Wilderness Adventures is the only book that has something on this topic – the ambush rules. However, they are limited to, well, ambushes and the maximum encounter distance is only 15 yards. This is not generic at all. Let’s expand the surprise rules from DFRPG Exploits with the concept of encounter distance from ACKS II and Terrain Rating from GURPS Mass Combat. I think these rules work, but I may adjust them in the future if I find something off.

Step 1 – Determine maximum encounter distance
When a random encounter occurs in the wilderness, roll on the Wilderness Encounter Distance table to determine the maximum encounter distance (MED) in yards at the start of the encounter, or he may use the average value instead. The encounter will then occur at either the maximum encounter distance or the maximum visibility distance (see below), whichever is less. It is also possible to achieve surprise and decrease the actual encounter distance further. The maximum encounter distance accounts for geography and foliage, while the maximum visibility distance accounts for lighting and weather conditions. The GM will then choose or randomly determine the direction of approach based on the terrain. In case of large groups, the encounter distance is the distance between the closest parts of the groups.
 

Wilderness Encounter Distance Table

Terrain Type	Max (Average) Encounter Distance	Terrain Rating
Barrens (any)	4d x 10 yards (140 yards)	3
Desert (rocky)	6d x 30 yards (630 yards)	4
Desert (sandy)	4d x 10 yards (140 yards)	3
Forest (deciduous)	6d yards (21 yards)	2
Forest (taiga)	3d x 5 yards (52 yards)	2
Grassland (other)	4d x 10 yards (140 yards)	4
Grassland (steppe)	6d x 30 yards (630 yards)	5
Hills (forested)	6d yards (21 yards)	2
Hills (rocky/terraced)	4d x 10 yards (140 yards)	3
Jungle (any)	4d-1 yards (13 yards)	0
Mountains (forested)	6d yards (21 yards)	2
Mountains (rocky/snowy/terraced)	4d x 10 yards (140 yards)	3
Scrubland (low, sparse)	4d x 10 yards (140 yards)	3
Scrubland (high, dense)	3d x 5 yards (52 yards)	2
Swamp (marshy)	3d x 5 yards (52 yards)	2
Swamp (scrubby)	6d yards (21 yards)	2
Swamp (forested)	4d-1 yards (13 yards)	1

 
Step 2 – Determine maximum visibility distance (MVD)
Usually, this is only relevant in open terrain or conditions that severely hamper sight. Maximum visibility distance should be calculated separately for each side in the encounter, making it possible for a small group to spot a large formation from far off.
Base MVD is 200 yards when spotting creatures or 3 miles when spotting terrain. When spotting fires, base MVD is 3 miles and no modifiers are applied.
                Modifiers: MVD takes -10% for each -1 of darkness and weather penalties, each SM below SM+0 of the largest target creature, and each level of Vision below 10 of the spotter. MVD takes +10% for each SM over SM+0 of the largest target creature, and each level of Vision above 10 of the spotter. MVD takes +50% when spotting a group of 10-30 creatures, +100% when spotting a group of 31-60 creatures, +200% when spotting a group of 61-240 creatures, or +500% when spotting a larger group. Obviously, the adjusted MVD cannot be higher than the distance to the horizon when spotting creatures (3 miles).
                Maximum visibility distance of terrain and fire is increased by elevation. For each full 4,000’ of elevation, double maximum visibility distance. E.g. maximum visibility distance to a bonfire on a 14,000’ mountain is 3 × 2 × 2 × 2 = 24 miles. Creatures do not necessarily become easier to spot with elevation.
                If you are using senses other than sight, apply only those modifiers that are applied to these senses normally.
 
Step 3 – Check detection and surprise
If none of the sides were being stealthy when the encounter occurred, the encounter occurs at MED or MVD, whichever is less, with no side being surprised. However, it is possible that both MVDs are lower than MED, and MVDs are not equal. In this case, the side with the higher MVD spots the other side without the other side spotting it and may evade the encounter automatically. If it decides not to evade, it may either begin the encounter at the lower MVD or try to achieve surprise (see below).
 
If one side was being stealthy when the encounter occurred and the other was not, the GM secretly rolls a Quick Contest of the stealthy side’s worst Stealth (or Camouflage, if the side is stationary and camouflaged) against the other side’s best Vision, Hearing, or Observation (if there are sentries). Do not modify the rolls for range! Incremental weather modifiers are calculated using the lower of MED and MVD. If the stealthy side wins with a margin of victory equal or higher than Terrain Rating, it achieves surprise and may reduce the actual encounter distance by 10% per point of margin of victory, rounded up (maximum reduction is 80%), or it may evade the encounter automatically. Otherwise, the encounter happens at MED or MVD, whichever is less, with no side being surprised.
 
If both sides were being stealthy when the encounter occurred, the GM secretly rolls a Quick Contest of their worst Perception-based Stealth. The winning side achieves surprise and may reduce the actual encounter distance by 10% per point of margin of victory, rounded up (maximum reduction is 80%), or it may evade the encounter automatically. On a tie, the encounter happens at MED or MVD, whichever is less, and both sides are surprised.
 
Altitude and Elevation: Regardless of terrain, flying creatures can start at an altitude of up to one-half the encounter distance. When encountering non-flyers in mountains terrain, the opposing sides begin separated by an elevation of one-half the encounter distance with the GM determining which side is higher based on the context.
 
Example #1
Side A: One SM+0 man with Vision 10, Stealth-10, not being stealthy.
Side B: Ten SM+0 orcs with Vision 9, not being stealthy.
Terrain: Hills (rocky/terraced); maximum encounter distance 150 yards; Terrain Rating 3
Conditions: daylight (no darkness penalty), drizzly (-1 per 50 yards to Vision).
 
MVD A: 200 yards -40% (-4 for drizzle) +50% (group of 10) = 220 yards. This value is higher than MED of 150 yards, so it doesn’t matter.
MVD B: 200 yards -40% (-4 for drizzle) -10% (Vision 9) = 100 yards. This value is lower than MED of 150 yards due to significant visual impediment.
 
The man (side A) spots the band of orcs (side B) way before they get a chance to spot him. He may automatically evade the encounter or try to achieve surprise. For the sake of demonstration, he tries to achieve surprise, even though that’s a stupid decision.
 
Side A rolls against Stealth 10, gets a 13; MoF 3
Side B rolls against Vision 7 (9 – 2 for drizzle), gets a 10; MoF 3
This is a tie, so the encounter happens at 100 yards with no side being surprised.
 
What if the rolls were different?
Side A rolls against Stealth 10, gets a 10; MoS 0
Side B rolls against Vision 7 (9 – 2 for drizzle), gets a 8; MoF 1
Side A has a margin of victory of 1, which is lower than the Terrain Rating 3. This wasn’t enough to achieve surprise in this terrain, so the encounter happens at 100 yards with no side being surprised.
 
What if the rolls were different? x2
Side A rolls against Stealth 10, gets a 7; MoS 3
Side B rolls against Vision 7 (9 – 2 for drizzle), gets a 15; MoF 8
Side A has a margin of victory of 11, which is higher than the Terrain Rating 3. This allows side A to decrease the actual encounter distance by up to 80% (10% per point of margin of victory, capped at 80%). Thus, the minimum encounter distance becomes 100 x 0.2 = 20 yards. Side B is surprised.
 
Example #2
Side A: One SM-2 halfling with Vision 12, Stealth-12, being stealthy.
Side B: One SM+1 ogre with Vision 9, Hearing 10, Night Vision 4, not being stealthy.
Terrain: Grassland (steppe); maximum encounter distance 690 yards; Terrain Rating 4
Conditions: dusk (-1 darkness penalty).
 
MVD A: 200 yards -10% (-1 for darkness) +10% (SM+1) +20% (Vision 12) = 240 yards. This value is lower than MED of 690 yards, so the actual encounter distance becomes shorter.
MVD B: 200 yards -20% (SM-2) -10% (Vision 9) = 140 yards. This value is lower than MED of 690 yards, so the actual encounter distance becomes shorter.
 
Here, the halfling may automatically evade the encounter with the ogre because he spots the ogre way before the ogre spots him. It’s nice to be a short king.
 
Example #3
Side A: One SM-2 halfling with Vision 12, Stealth-12, being stealthy.
Side B: One SM+1 ogre with Vision 9, Hearing 10, Night Vision 4, not being stealthy.
Terrain: Forest (decidious); maximum encounter distance 20 yards; Terrain Rating 2
Conditions: dusk (-1 darkness penalty).
 
MVD A: 200 yards -10% (-1 for darkness) +10% (SM+1) +20% (Vision 12) = 240 yards. This value is higher than MED of 20 yards, so it doesn’t matter.
MVD B: 200 yards -20% (SM-2) -10% (Vision 9) = 140 yards. This value is higher than MED of 20 yards, so it doesn’t matter.
 
See? MVD only matters in open terrain. Here, the halfling cannot avoid the encounter that easily. Let’s check detection.
Side A rolls against Stealth 12, gets a 9; MoS 3
Side B rolls against Hearing 10, gets a 6; MoS 4
Side B wins, meaning that the halfling is about to get clubbed. No surprise is achieved, and the encounter starts at 20 yards.