Most fantasy enthusiasts would agree that world-building is vital for the life of any particular novel. Just like a character, the landscape itself should have dramatically vivid attributes that define it and set it apart from the monotony of average fields, mountains, rivers and seas (and even those can come alive with the right details). An imaginative author can design a world that is as memorable as some of the best characters of that genre.
Fortunately, there’s a lot of material to work with–much more than just an array of flora and fauna which may or may not be alien. Worlds have scars and weather patterns (consider Sanderson’s Way of Kings and the brilliant world defined primarily by its volatile storms and wind-hardened creatures).
Think also in terms of cartography. What makes Kevin Anderson’s Terra Incognita series so intriguing? Or The Voyage of the Dawn Treader? Even the inhabitants of that world don’t know what lurks over the horizon. It makes for some wonderful suspense. Some authors think big, taking in whole atlases and mythologies; some think small, ruminating on an old building or focusing on one city in great depth.
Wrapped up in all these considerations are seasons, animal behavior, abnormal catastrophes, storms, etc…and above all: Culture. The world is tied inseparably to the people and the people to the world. How do they shape each other? The fantasy/science fiction author has to become a biologist, and archeologist, a historian, and an anthropologist all at once. Not to mention a psychologist and a linguist. The best writers employ a whole college of disciplines.
We fantasists have to be as much in this world as anyone else. We have to be paying attention. Doing research. Learning, jotting stuff down, and drawing maps. The best imaginary worlds are still tied to ours in important ways. There are no rules, but there are guidelines.
This brings us to the wonderful paradox of fantasy. Readers need some realistic grounding and will therefore complain if a world has no anchor in reality. If the seas are made out of toxic wastes, the fish better be monstrous creatures who can breath it. If the whole world is covered in snow, people won’t be wearing sandals. Usually a fantasy world will have great similarities to ours with only small, plot-defining differences. It’s easy to get out of hand. It’s easy to forget the world for the story and both suffer from malnutrition.
Landmarks are a good way to avoid loosing readers. Reminding them of that unstable volcano in the vicinity of the spider-infested forest where the action is taking places could be a beneficial detail–especially if you plan on making the lava flow later. Introduced landmarks should be used, should become part of the plot. One of the most common complaints about certain fantasy authors is that they’ve become over indulgent to the world they’re creating, adding details that don’t add to the understanding of the information important for the plot. This is a fuzzy line, but when an author’s writing for themselves it’s noticeable.
The best fantasy authors can develop a world that gives readers a sense of it’s vastness or character without throwing out unnecessary details. Here’s a panoramic view of Middlearth that Tolkien gives us in The Fellowship of the Ring. It’s good stuff:
“It was now as clear and far-seen as it had been veiled and misty when they stood upon the knoll of the Forest, which could now be seen rising pale and green out of the dark trees in the West . In that direction the land rose in wooded ridges, green, yellow, russet under the sun, beyond which lay the hidden valley of the Brandywine. To the South, over the line of the Withywindle, there was a distant glint like pale grass where the Brandywine River made a great loop in the lowlands and flowed away out of the knowledge of the hobbits. Northward beyond the dwindling downs the land ran away in flats and swellings of grey and green and pale earth-colours, until it faded into a featureless and shadowy distance. Eastward the Barrow-downs rose, ridge behind ridge into the morning, and vanished out of eyesight into a guess: it was no more than a guess of blue and a remote white glimmer blending with the hem of the sky, but it spoke to them, out of memory and old tales, of the high and distant mountains.” – Chapter 8, The Fellowship of the Ring
It sets the scene for the impending adventure. Tolkien uses colors, the placement of the sun, names of places, and all the points of the compass to paint before us a tapestraic picture of a world that seems more real every moment. It puts you there. That’s the key to world building: make it real to your readers. Transport them to the world.