I was surprised no-one had responded to you yet. In my campaign I was just trying to work through that information, too.
In 3.0, there were some rules in the DMG (sorry cant' remember where, maybe the "Encounters" section or something) there were rules for trying to spot someone waiting in ambush for you. It was something like checking spot once at the max distance against a 25, and then again at half the max distance.
Looks like in 3.5, it's simply based on terrain (which determines max distance, for example 2d6X10 in rugged hills), and on the spot check (at -1 per 10 feet of distance).
So, just to work it through, (like I will need to do in my upcoming game). My group of Orcs is walking through the hills, as is the party, who are hunting for orcs.
I'll say the Orcs are taking 10 on a hide check, but moving at normal speed, cause they aren't expecting immediate trouble. So, they have a hide score of 10 -5 for moving + 0 for hide skill = 5
I'll say my party is hunting for orc, so they should be hiding (but I'm just going to take 10 for them, as they will be creeping through the hills for several hours), and moving at half speed, waiting for trouble. They'll be a hide of 10 + 0 for half-movment + 3 for the worst hider's skill (shoulda left him at home!) for a hide of 13.
I'm also going to say both groups are simply taking 10 at spot, as otherwise, this could take a while.
The best spotter in the Orcs would have a spot check of 11 (dumb orcs) This would mean they'd never spot the party until they stepped on them. This would be where I'd invoke some common sense, and say that if the party's going to attack, they'd get to start the combat (with a surpise round) at 20 feet from the nearest orc. If the party doesn't start combat, the orcs walk on by. If the party then wants to follow, they'd have to speed up their movement, and they'd have a hide of only 8 (-5 for moving full speed). The party would have to stay back a distance to not be spotted. 11 - 8 = 2 at least 20 feet, but they couldn't be sure how good the orcs are (and 20 feetish range is a range I'd start checking listen checks), so they better stay back as far as they can and still see the orcs 13 - 5 = 8, which means 80 feet. Since 80 feet is within the maximum max distance in rough hills 2d6X10 = 120 feet, they should be able to trail them effectively.
If we make this more challenging, and throw a good Orc spotter (maybe a ranger or something) in the mix, and up the Orc's spot to 10 + 7 for skill = 17, then things change little.
If the best spotter in the party as a +6, the 16 is the spot take-ten, and the party would notice the orcs at 16 (spot) - 5 (orc's hiding) = 11 means 110 feet.
The orcs would notice the party at (17 (spot) - 13 (party's hide) = 4) 40 feet.
Clearly, the party would see the orcs first, and could plan accordingly, but it's possible that the orcs would be heading away from the party, and the party's only moving at half speed. Will they speed up? hmmmm....
However, since the max distance in hills is 2d6X10, and say I rolled 30 feet, it's possible that they run into each other, both surprised, and start combat.
*sigh* That seems like a lot of work. I'm going to go make a spreadsheet for all this.
And to think that you have to do all this crap for listen and move silently, too.
pvandyck
