One of the biggest challenges for a DM/GM is managing things that can be measured. I'm talking about time, distance, height, width/span, etc. The real tricky one is time, which can be moving faster or slower in the real world than in the campaign world. In today's blog, we are going to talk about distance.
Size matters! For a genuinely unobstructed view, lookup. You can see the Andromeda galaxy with the naked eye on a clear night, which is 2.5 million light-years away – that's 15 quintillion miles. The typical adventuring party is not looking at the stars; they are looking at the next threat or figuring out how far that village is from the hilltop they are standing on. The DM/GM should give them a fairly reasonable estimate. Relating your estimates to the real world and being consistent throughout the campaign helps maintain the immersive experience.
So how far can the human eye see something like a village or a pack of Gnolls running toward them? The human eye, about five feet off the ground, can see three miles. That assumes both you and the Gnolls are on a flat surface with no obstructions in broad daylight. You can use three miles as your rule of thumb and start reducing the distance from there. If the party is on a hilltop, they will see even further; the trick then becomes can the party identify what it is they are seeing. Tie to roll a D20!
Not to get too far off-topic, but 3 miles is equal to 15,840 feet. The gnolls have a move rate of 30 ft per round or 30 ft every six seconds. Let's do a little math. 15,840/30=528 So you have 528 rounds or 3,168 seconds, just under one hour before they arrive! A party can do an awful lot in one hour.
But what if it's dark? Ok, let's assume the Gnolls are carrying torches. Unfortunately, no one has studied how far away you can see torchlight, but they have studied candlelight. The farthest distance a human eye can detect a candle flame 1.71 miles! That distance was calculated by a pair of physicists from Texas A&M. Again, you have to be looking for that light, and there can be no obstructions in the way.
How can I be sure they are Gnolls and not the hoped-for reinforcements from the militia in the village? Well, you can't! Even though you can see them from that distance, you won't make out who they are until they are much closer. Scientists from the University of California and the University of Washington found that after 25 feet, face perception diminishes. At about 150 feet, accurate face identification for people with normal vision drops to zero.
You probably think I have been giving you some pretty interesting trivia, but how can I use this information to make my game better. Good question? I have looked for some tables that would help the DM/GM and come up dry, so we are developing some for our Copernia Campaign World. Until then, you can have fun with the information I have provided and do some experiments of your own.
Did you know that your arm is about ten times longer than the distance between your eyes? With
a bit of math, that fact can be used to estimate distances between you and any object of approximately known size. The information below is from the Old Farmers Almanac (8.2017)
Imagine, for example, that you're standing on the side of a hill, trying to decide how far it is to the top of a low hill on the other side of the valley. Just below the hilltop is a barn, which you feel reasonably sure is about 100 feet wide on the side facing you.
· Hold one arm straight out in front of you; elbow extended, thumb pointing up.
· Close one eye, and align one edge of your thumb with one edge of the barn.
· Without moving your head or arm, switch eyes, now sighting with the eye that was closed and closing the other.
· Your thumb will appear to jump sideways as a result of the change in perspective.
· How far did it move? (Be sure to sight the same edge of your thumb when you switch eyes.)
Let's say it jumped about five times the width of the barn or about 500 feet. Multiply that figure by the handy constant 10 (the ratio of the length of your arm to the distance between your eyes).
Now you get the distance between you and the barn—5,000 feet or about one mile.
The accompanying diagram should make the whole process clear.
With a bit of practice, you'll find that you can perform a quick thumb-jump estimate in just a few seconds, and the result will usually be more accurate than an out-and-out guess. At a minimum, it will provide some assurance that the figure is in the ballpark—which, in many cases, is as close as you need to get.