I usually just describe what the players see verbally... And it's up to them to draw their own map. It happens every so-often that the players screw-up the map and get lost anyway.
I still use my nifty magnetic-eraseable-white-borard-with-a-permanent-pre-made-one-inch-grid to draw up those wierd areas too complicated to describe. I also use it for every battle; drawing up the immediate surroundings and using magnetic letters and numbers to represent those in the melee.
Ultradan
I play with a large, easel sized pad of graph paper. I am about to run my group through a large subterranean area. Is there a generally accepted way to keep your player "in the dark" so to speak?
I'd love to be able to keep the details (rivers, stairs, walls, etc.) hidden if I can, I am just not sure if there is a practical way of doing this.
Has anyone out there discovered a good method for mapping in the darkness?
. . . other than that awesome projector set-up that makes me want to wet my pants every time I see it.
I use Tac-tiles and generally just draw what my players can see. It slows down the dungeon-delving a bit, but not tremendously so. It also helps that my group is the kind to not go past any doors/hallways for fear of getting ambushed from the rear (the early Shackled City adventures put that fear into them), so the amount of backtracking is minimal. The great thing about Tac-tiles is you can pick up ones you've already used, wipe them off, put them where the party's going, and start drawing again.
This requires pretty good knowledge of how far a given character can see in the dark, or with the assorted light sources out there. Generally though, you'll find a corridor rarely extends farther than an elf can see with a sunrod (60' clear, 120' shadowy). For shadowy areas, I'll draw walls but not terrain features, instead giving a verbal description (you see a large solid object in the center of the room. From here, you can't make out any details.
If you want to draw out the entire thing in advance, you might consider making some cover-up sheets of construction paper (I prefer construction paper because it's thick enough that the writing underneath won't show through). Make sure you use small enough pieces that you aren't giving away the size of a room by the sheets covering it, and lay the construction paper cover sheets out so they'll come off in the order you expect the PCs to enter a space by (the sheets will overlap a bit, after all).
Because you don't want to rip your map when removing the cover sheets, you may want to consider laying some clear tape on the map itself to make a plastic taped spot, then taping the cover sheet to the taped spot and not the paper itself.
If you have secret doors and the like, best not to include them on the map at first, and quickly draw them in when they're discovered; there's no good way to show a wall but hide the door you've already drawn on it.
...And UltraDan, I would love to let my PCs map out what I am describing, but there are going to be a lot of twisting tunnels and odd shaped caverns in the upcoming adventure. I might try and implement this idea at an easier time.
Actually, it's the perfect time to do this experiment. Just imagine how difficult it would be for YOU to accurately map a real twisting sewer tunnel in real life... The player's map SHOULDN'T be perfect. As long as they can figure out that tunnel C somehow connects with room H because they've been there before, that's what's important. The player's map should be ugly as hell.
Also, it's kind of fun to compare maps (Players and DMs) after the adventure is over to see the differences.
Ultradan
I use a fairly large (3' x 4') wet-erase map by Chessex. I use hand-painted minis (after 20 years, I'm pretty good if I do say so myself) and draw the map out as the group progresses. While this does take away to a certain extent from the players having to do their own mapping, once we get past a point where I have to erase and redraw, I make them tell me what they do when they get to certain points. Since they can usually visualize what I drew, it makes it reasonable and we don't wait around while one player draws out the map (which, as UltraDan said, can be fun, but slows the pace of the game down in my experience).
In general, I keep track of the range of the light sources and Night Vision/Darkvision (I just remembered the other day that the NPC Paladin is an Aasimar and can see in total darkness - something she's not done since the campaign started - D'OH!). Once I know what the light sources are (usually a sunrod and a Light spell cast on a holy symbol), I draw out to the maximum distance visible at the time, including shadowy light and lay a marker across the table to show how far bright light goes vs. how far they can actually see. I then do as was suggested before, describing shapes, rather than details if the items are in the shadowy areas.
One neat bit about this - A Rogue can hide literally 5' away from the regularly-lit area and Sneak Attack if the PC doesn't make his Spot check (which I make for them in those circumstances. "Roll Spot for me" tends to get, "I draw my sword and look around!" though it's usually not QUITE that much meta-gaming). Thus, my players know that, while they can see the map out to maximum distance, their characters can't see it as clearly as the players can. It works out nicely, actually.
I use a combination of the techniques described above. I use two of the regular DMG/Minis Battlemap Grid, but with Two sheets of 2x3' plexiglass, (which can be dry-erase markered to death)over them. This is a lot of area for outdoor encounters and if less is needed, well, then the players get to put their books down on the table instead of holding them out at arms length for the duration of the session *sly grin*
I recently started to use the big easel pad with the one inch grid to pre-draw some of the more convoluted encounter areas, but I still use the plexiglass to dry-erase marker in features like damage from combat, busted doors, corpses littering the battlefield, and of course, the perennial fave, the secret doors & traps.
So far it works well, and since use of player knowledge is punishable by successively worse blue bolts (in increments of 3d8)I don't often have to use cardboard or foamcore to cover undiscovered areas (although I still do, sometimes if only for suspense) and areas they have been through. For GURPS, I prefer the chessex mats, but for some reason, they never caught on with my D&D group.
Groups I've gamed with in the past have used white boards set up horizontally to be the floor. We've also used the surface of glass tables and just used erasable marker on those (and cleaned it up afterwards to avoid annoyed parents/siblings as the case may be) Paper like that used by architects (I think) has worked as well. For combatants we used coins: pennies or nickels for meat shield/mobber creatures, quarters for lieutenants (or leftenants, British spelling) and, being Canadians and having these coins available, loonies ($1) or toonies ($2) coins for main monster/BBEG characters, since we have very few minis around and a few of the ones we do have go to our characters.
I have a CHessex pad myself, but I also tend to print out some key maps in my campaign, TO SIZE. It's a bastard, I know, but once I tile them together (thank you Grpahic Design school for deez skillz!) I got a whole big map with all the funky things I want on it.
If I'm hding stuff, then I either print the overlay ( I had under ground map that was 4 photo paer sheets thick!) to cover them. In the old days, we used to just over the dungeon section by section wiht a solid paper or board and as you looked you took away bits here and there.
Also describe stuff all the time. I'm constantly saying stuff, but not with figure, like "He's about where your car is right now" and then they make adjustments in thier head like a hundred feet, etc.