Random Terrain Features: How do they work?

[Gez]

I'm kinda confused by the DMG section on Wilderness Adventure. From page 87 (DMG 3.5) on, there are percentile tables for features of various terrains.

For example, here's the first one, "Forest Terrain Features:"

                    ---Category of Forest---
                    Sparse   Medium    Dense
Typical trees         50%      70%      80%
Massive trees         --       10%      20%
Light undergrowth     50%      70%      50%
Heavy undergrowth     --       20%      50%

How do they work?

1. Roll once for each line. A square of dense forest has a 80% chance of featuring one typical tree, a 20% for a massive tree, a 50% for light undergrowth, and a 50% chance for heavy undergrowth. (Which amount to a 4% of having all of those.)
2. It's a problem of inconsistant format. If it followed the same presentation as all other D&D percentile tables, it would be like this:
   

                       ---Category of Forest---
                       Sparse   Medium    Dense
   _TREES_______________________________________
   No trees             01-50    01-20      ---
   Typical trees        51-00    21-90     01-80
   Massive trees         ---     91-00     81-00
   _UNDERGROWTH_________________________________
   No undergrowth       01-50    01-10      ---
   Light undergrowth    51-00    11-80     01-50
   Heavy undergrowth     ---     81-00     51-00
   
   (Roll once for trees and once for undergrowth.)

3. Something else?

 

[cmanos]

you, as the DM, define the area as Sparse woods, Medium woods or dense woods.

Say you decide on medium woods.

I'd roll first for trees, then go back and roll again for underbrush in those squares not occupied by a tree.

Specifically, I'd make up a spreadsheet that generates two random numbers per square and places a symbol in each with a tree or undergrowth.

 

[Elder-Basilisk]

Unless you're drawing a random map by computer, rolling for each square is a complete nonstarter. Even with a small battlemap, you'd waste a half-hour of play time just laying out the battlefield.

I think the reason it's expressed in percentages rather than rolls is because it's intended as a guide to drawing out maps. In medium forest, roughly 10% of the squares should have massive trees in them (which works out to about one massive tree in every 3x3 area of the grid). So draw in a lot of them. 70% of the area will be light undergrowth so don't draw any in. Instead, draw in the 10% clear area and the 20% heavy undergrowth area. (Which roughly correspond to saying about as many clear squares as big trees and twice as many dense thickets).

If you look at it as a guide to varying your terrain rather than a table to roll on, I think it becomes a good deal more useful to anyone who isn't writing software.

 

[Plane Sailing]

I think the reason it's expressed in percentages rather than rolls is because it's intended as a guide to drawing out maps.

< snip>

If you look at it as a guide to varying your terrain rather than a table to roll on, I think it becomes a good deal more useful to anyone who isn't writing software.

Exactly right. That's why the percentages don't add up either - different features overlap.

It is a great help IMO just to give Dms an idea of roughly what proportion of space to allot to each kind of terrain feature when scribbling down a random encounter map.

Cheers

 

[dcollins]

2. It's a problem of inconsistant format. If it followed the same presentation as all other D&D percentile tables, it would be like this:

I agree with this interpretation, that's how I've been reading it. (Of course rolling for each square is unworkable in practice at the table, but that's what is written there.)