I will then consider the avenues and barriers between them. In this case, for my example, I think I will create a triangle of pathways since there are three strategic locations. Between the ‘The Head of the Pass’ and ‘The Harbor’ I will have an avenue that one day will become a road but in the beginning starts out as an animal trail. I will also add a barrier, which is a forest that may be populated later with any number of beasts, or villains. The avenue therefore passes through the forest which sets up that pathway as having an avenue and a barrier. I like to combine them.
Between ‘The Harbor’ and ‘The Tall Hill’ I will put another avenue. This time I will have a river as a barrier, which at first cannot be crossed except by fording, or swimming, but later I imagine there will be a bridge built at the ford. This avenue will be little traveled for a long time, until there is a town placed on the hill and the harbor discovered. That may take many centuries. So that pathway also has one avenue and one barrier. So far so good.
Between ‘The Tall Hill’ and ‘The Head of the Pass’ I may put only a barrier to create a challenge for later and keep things interesting. Let’s say a peat bog. And how about a nice big mountain lake, in which dwells a monster, or perhaps a band of Nixies? That will make for some fun adventures later. I might even put a treasure at the bottom of the lake. How about a rare magical gem that happens to have fallen from the mountains there? If one day a hero should slay the lake monster, or defeat the Nixies (I have not decided which yet, and maybe I'll have both), then the gem might be found, and a new magic item for the World crafted from it. Could happen!
So to get to ‘The Tall Hill’ from 'The Head of the Pass' one must go to ‘The Harbor’ and then cross the river, or one can dare to attempt crossing the peat bog (a bad idea, probably, unless you happen to be an an especially hearty adventurous sort).
So at this point I have this:
I am now able to begin developing a history of this region. I can begin it quite arbitrarily, actually, by posing that there are three primary races that occupy the region. The first comes from the West, and occupies ‘The Tall Hill’, and I’m going to say this is a hearty band of farmers who decide to start planting along the lower rim of the hill at the base of the fruited plain, wisely led by some priest of the Elkron of the Earth to do so, no doubt. Eventually that Hill may become a Fortified City, but at first it is just a poor little hill town trying to eek out a living along the edge of the plain.
At the same time, a hero of a band of Elves living in the forest for ages is taught fishing by the Elkron of the Sea, and so decides to occupy the rocky land on the north shore of the harbor. He and his ilk eventually create rafts to help them fish and ferry, and go on to become boat builders, and are destined to rule the seas thereabouts (unless something goes horribly wrong for them - don't laugh, it could happen). And so the Elves split into two tribes, one of the forest, and one of the sea.
On the pass, I will put two small warring tribes, say of Ogres and Trolls. These folk are only semi-intelligent, but use a rude form of earth magic, and can hide in the ground, mostly occupying caves and waterfalls. They're cruel and hunt anything that moves. Fortunately for the region neither tribe is very large, and they mostly feud with one another, and leave everyone else alone. Unless they get too darn hungry, in which case some one or a few might venture down the slopes.
On the other side of the pass is another rich land with many wonders to be discovered one day… but not for a long time, no doubt.
And so it came to pass that the Elves of the Sea met the Farmers of the Plain, and began a mutually beneficial trade of fish, and produce. Things progressed and eventually two towns were built up nicely, Hill Town and Harbor Town. At some point they collaborate on building a nice stone bridge over the river. All is well.
This mutually beneficial relationship worked very nicely for a long time, until one day an ogre of ill repute, and worse manners, wandered hungry from the mountain. First trying the peat bog, he lived a rough existence for some time, until he’d hunted all the game there. He moved on, wretched creature, until he came to the forest, in which he dwelled for some time with his equally loathsome wife. This began to impact the Elves as they recognized a change in the forest, and were loath to go there, since the Ogre was very cruel, and powerful, and his wife was even more so, and a mystic of evil intentions. The northern forest began to be populated by wolves, and bats, and stinging insects, and storms gathered over it, and it became brackish and unwholesome. It was then, finally that the Forest Elves decided it was high time to send some hero or other to rid the wood of the Ogre. But who would dare to face such a grizzly couple as the Ogre and his wife?
And so, we have a basic setup for a Campaign. It was not very difficult, once the groundwork had been laid, and things followed along rather easily after that. And so, for those who wish to create their own Campaigns it is not so difficult really. It just requires considering a few aspects of the geography, the history, what races, and adding some history. Of course, this is a very simple and basic example, from which a lot more history and whatnot could be derived, and you can consider that the Campaign action could take place anywhere along the timeline. Note that if you do chose to pick a middle spot in your timeline then that would give you the ability to provide foreshadowing or perhaps "prophetic" insights to the Player Characters along the way, as well. Not a bad option, if you do so with discretion and care.
The next thing I would do to fill things out further is create the Primary Non-Player Characters of the Region. I would consider the King of the Ogres, the King of the Trolls, the Lord of Hill Town, and the Lord of Harbor Town. I would create Non-Player Characters for each, and their immediate families, whomever is important and plays a role in the setting, such as the Hill Town Lord’s selfish wife, or his heroic eldest son perhaps. I would create a few colorful NPCs to fill in the towns a bit. Some of them would be famous for something, while others would be ordinary folk, such as the corner baker, his daughter, and the local snake oil peddler, and his ilk. And so on.
Over time once I've filled in the towns with various NPCs, and given them little histories, and some aspirations, perhaps, I would then add villains, a few monsters or really rotten people to spice things up, and then finally add the essential important artifacts over which the people squabble. Is there hidden gold in that there Hill? Is there a magic sword that the Elkron placed anywhere as a Seed of Destiny? Is there a wizard who has created magical artifacts that have created troubles here and there? Or a famous sword smith who happens to be very talented at his craft but whose dark sense of humor has infected his swords with a curse of some kind? All of these things will get added to the setting over time.
And voila, the Campaign setting is ready, and even has something of a life of its own. Now when the Player Characters go adventuring in the region there is an underlying layer of coherence to things, a story that is already going on beneath the immediate concerns of the Player Characters, and so the world has a much better chance of feeling ‘real’ for them than otherwise. This is what I have found works for me.
And that’s generally how to go about creating Campaign settings, more or less. When you want to go whole hog, you can also add mythic dimensions to your Campaign (I often try to do this) by reading classical literature, mythology, old folktales and fairytales for inspiration. Works like a charm! :)
Best wishes on your Campaigns!