Before going too far down the path of picking the area’s primary settlement and detailing it, we need to step back and consider the area’s terrain and climate. These will be factors for other decisions to be made. If you’re taking a top-down approach, you might have already detailed these factors. In this case, the important thing is to choose a location for your local area with the climate, terrain, population, government, etc. that fits the stories and adventures you want to have.
But if you haven’t put together any details for the larger area you still have a blank slate. While some people might suggest picking these attributes randomly from a list, it is better to consider the types of stories and adventures you plan to tell. If one of the group’s possible adventures is an abandoned mine, you need to have a mountain with a mine entrance nearby. If your campaign is going to stress the harshness of the elements, consider that when deciding on the area’s climate. Also remember that these two factors, terrain and climate are related. For example, tropical or temperate forests can’t be on a high mountaintop and even pine forests won’t be on an extremely high mountaintop.
In either case, the local area should be about 40 to 50 miles across which represents a reasonable day’s walk in each direction from the center.
Keep in mind that your local area may have a few different terrains, although it probably only has one climate. The area may have a prairie, but with a forest area near a river that runs through it. The river may flow from a small mountain range that is forested.
If several different widely varying terrains and climates fit the stories you plan to tell or if you haven’t thought about any stories where these factors matter it doesn’t hurt to look at a list for terrains and climates. In fact, looking at these lists may spontaneously generate some stories in your mind. If so, choose the options that seem to have the most or best story leads. If you’re still stuck, force yourself to randomly point at one option and think about it for a few minutes, keeping in mind Dungeoncraft rule #2.5: Some of the best background stories come from explaining something that isn’t obvious in your campaign world.
With rule #2.5 in mind, you might look at the terrain options and think about a story to explain them. For example, if you consider “island” and “mountain” you may think of why the island has a mountain. That thought might lead you to think the mountain is actually a volcano, but you didn’t choose “volcano” from the list so you consider it a dormant volcano. That thought leads you to thinking of why the volcano went dormant. One explanation might be that the fire elementals that lived there long ago were killed by a group of heroes. Now your region has an interesting backstory that may lead to more adventure ideas.
Don’t be afraid to steal other maps, real or fantasy especially if you just use them as a guide and redraw them yourself. There are many ways to draw your wilderness maps, but there are hex map brushes for GIMP if you like that map style.
Regardless of your map style preference, computer software and the internet makes it very easy to have maps with several layers for displaying different sets of information. For example, you can draw out the basic terrain as your base background layer. Then add a layer for political boundaries. Add another layer for roads. Add another layer for secret/undiscovered locations. Add another layer for showing land contours. You should be able to re-order and turn on and off these layers as needed (or work from the same base map and make separate maps from the one base map) to prevent others from seeing all the secrets or to simply prevent information overload.
Varied terrains include: Jungle, Grasslands, Farmland, Light Forest, Heavy Forest, Forested Hills, Rocky Hills, Mountain, Mountains, Volcano, Badlands, Cactus Scrub, Heavy Cactus, Rocky Desert, Sand Dunes, Sandy Desert, Swamp, Marsh, Shoals and Reefs.
Almost all settlements will be located near some source of water: an oasis in a desert, a large or small river, the mouth of a river opening to a larger body of water, where multiple rivers join, large or small lakes, along a coastline, on an isthmus, on a peninsula, or an island.
If you are adding further detail to a larger area map, you’ll want to match the terrain and climates indicated on the larger map. But keep in mind that these aren’t satellite images so if you want to change things a little to better fit your setting, feel free to do so. It is easy to explain the differences as mistakes made by whoever created the maps.