Starting the Adventure Maps

First Things First

Start your adventure maps by making a list of locations you know you'll need somewhere on the map. For now, concentrate solely on the locations that are absolutely essential to the adventure. For instance, if the adventure is centered around a quest for a magical item, you'll need the location in which the item is finally found. Similarly, if your adventure calls upon the player heroes to investigate an underground war between goblins and kobolds, you'll probably need several areas housing the two combatant tribes.
The best way to guarantee that you've correctly identified all your requirements is to mentally strip your adventure down to its barest elements so you can make sure to account for all these elements when you draw your map. For instance, "Party enters ruined stronghold looking for fabled magic sword; party discovers that a tribe of hill giants has established a lair in the stronghold; leader of the giants uses the magic sword as a table knife, unaware of its value." Or, "Party enters dungeon to rescue a princess kidnapped by an evil cult; princess faked the kidnapping and is actually the cult's leader; she and her followers hoped the ruse would lead her father's champions (the party) into a trap." In the former case, your map would need quarters for the hill giants, especially the king's kitchen (where the sword is found). In the latter case, you'd need one or more areas that make up the cultists' trap.
My own adventure reduces down to "Party begins as prison laborers for a band of orcs; orcs are forcing the prisoners to dig through the remains of a ruined temple to find some mysterious object; the party is trying to escape." For my adventure, I need:
A semi-hidden vault (the orcs believe their quarry is located in one of the temple vaults). Some rubble-strewn work areas the orcs' prisoners must dig through to reach the vault and the orcs' prize. Prisoner confinement areas and barracks for the orcs (both improvised atop the temple's original facilities). Since escaping from the orcs and the temple is the main objective of my adventure, I'll also need to include a number of possible escape routes on the map. In an earlier installment, I noted that it's a good idea to include alternative approaches to overcoming an adventure's obstacles whenever possible. Since the escape is such an important goal in this adventure, I'm especially determined to provide the players with a good set of multiple choices. Therefore, in addition to the obvious main entrance, I've decided that there are a few hearths in the temple featuring chimneys that stretch up and out of the complex. Later on, to make the players' choice of routes more interesting, I'll try to position the chimneys such that each offers its own unique challenge.

Scouting the Locations

Once you've identified all your needs, the next step is to expand the list to include locations you'll want to place on the map. For me, this is usually a two-step process. First, I try to look at the setting from a logical perspective and ask myself what sort of locations should be present. The notion of a ruined temple, for instance, implies that some of the rooms in the complex once served as shrines, meditation chambers, and quarters for the priests and their servants. Similarly, logic dictates that if the temple once served as a living area, its inhabitants needed access to food, water, and other basic necessities, leading me to place ruined kitchens, pantries, and water storage areas on my list. Because my backstory states that the temple was originally constructed as a sort of citadel to house an important artifact, it also seems logical that warriors or guardians (paladins, in this case) were quartered in the temple alongside the priests.
At this stage, I also flip through the Monstrous Compendium® books and their various supplements to start thinking about the sort of creatures I'll call upon to populate the map. Although it's unnecessary to draw up an exhaustive list of occupants at this point, some monsters have special requirements for their lairs that I'll need to take into account when drawing the map. In this case, I decided that large spiders, stirges, and wild dogs are ideally suited to inhabit the temple ruins alongside the orcs.

Drawing the Map

Once the list of locations is complete, it's time to start drawing the actual map. Begin by deciding upon a couple of basic parameters. How large do you expect the map to be? How many "dungeon levels" will it cover? And, what (if anything) serves as a main entrance?
In my case, I decided that my map would consist of a single level that should cover roughly one sheet of graph paper with fairly small squares. As a general rule of thumb, you can assume that each full page of dungeon maps that are part of your adventure translates into approximately two game sessions of playing time. Two evenings sounded just about right for what I was trying to accomplish. My main entrance, I decided, would consist of a long staircase descending down into the very center of the complex.
When drawing dungeon maps, I always start by lightly sketching a very general outline on the graph paper. In this case, I noticed that most of the locations I identified fit into four general categories: priest quarters, temple rooms, special areas (the key room, paladin quarters, and wizard labs), and the monster maze. I drew a rough box the approximate size of the complex centered around my main entrance, divided the box into four quadrants and lightly labeled each to correspond to one of the location categories. I decided the monster maze would occupy the northwest quadrant of the complex, the temple areas would occupy the northeast, the special rooms the southwest, and the priest quarters the southeast. I then lightly penciled in the names of all the locations I identified in the exact areas in which I wanted to place them on the map.
With this guide in place, it was then a simple matter to sketch out the temple's various rooms and corridors. I placed all the locations I'd already identified in the rooms that ended up closest to the locations I'd already sketched out for them. By the time I was finished, of course, the map contained more rooms than I could match to my list of locations. To decide what to do with these "extra" rooms, I was forced to double and triple up a few general locations like the priest quarters and meditation chambers. I also thought up a few more locations to occupy some of the gaps, a process that was a lot easier now that there was an actual plan for the complex in front of me.