In your fantasy novel, a character walks into a room. It's an office of some kind, perhaps that of a petty official in the service of whatever government rules the land. You describe the room – a desk, chair, cupboard, window. It’s generally spartan, no decorations, a few maps on the wall, a small wooden box set neatly on the desk. This box will be never be mentioned again. It’s not part of the story, and you only include it in your description to indicate that the office, while bare, is in use.
Here's a question. What's inside the box?
Sure, the box is never opened, never comes into the story, and will be forgotten by the lead character the moment he/she leaves the room, but does that mean it's unnecessary for you, the author, to know exactly what the box contains? Is this a vital detail – or is it just something you can skip over while you move onto the exciting parts of the story?
Imagine, for the sake of argument, that you have given consideration to the contents of the box. It contains a writing kit – two quills, two bottles of ink, and a blotter. This is an office, after all, so it's no suprise to find it contains writing implements. Now you can forget about the box and move on.
Or can you? The thing is, if it’s a writing kit in the box, that poses a number of other questions. For one, what does the official write on? You’ve made no mention of any paper lying around, no books or documents. Why would a desk hold writing equipment if there’s nothing to write on? An office desk without paper seems odd, even in a fantasy world, and needs to be explained.
But does this society even have paper? Paper was invented by the Chinese sometime around the 2nd century AD, spread to the Islamic World, and reached Europe in the Middle Ages. Before that, expensive materials like animal hide (vellum, parchment) and even silk were used. Documents produced with these materials were greatly valued, and were the exclusive property of the rich.
If the society of your novel is pre-paper, that would go a long way towards explaining why there are no documents or paperwork on the desk. Perhaps the records this official handles are stored elsewhere, and brought in only when his attention is needed. Perhaps he hardly ever sees documents, and the writing kit is more of a badge of honour than a functional tool.
But if this is the case, why would there be maps on the wall? Pre-industrial maps were hand-drawn, and usually considered works of art in their own right. They also tended to be very large. Any pre-paper map that sits on your fantasy office wall is likely to be worth a fortune. Is it really going to be left pinned up on the wall of a minor bureaucrat's office? Unlikely, to say the least.
So, in order to maintain reality, the maps have to go.
But having established that your society is pre-paper, other questions need to be answered. For one, how is news exchanged in your fantasy world? It can’t be by newspaper, or letter (except by the rich), or posters in the town square. Could it be by town criers – people who journey from township to township, standing in the village squares and proclaiming the events of the land? Could it be by minstrels – music makers who compose songs about current events and sing them in taverns and other public places? If so, how do these minstrels and criers get their news? How do they travel? How current is the information they bring? What sort of news is it?
Again, none of this information may ever reach the pages of your story. Not directly, anyway. It will reach the pages of the story in other, more subtle ways, because this kind of isolation influences the way communities of people evolve and develop.
It’s easy for us to forget that widespread and easy communication is a very recent invention. In the pre-technological world, cities and towns needed to exist with a great deal more autonomy than modern times. It was either that or face extinction. If Grud Tonguestealer and his merry band of raiders decided to come out of the mountains and attack the nearest city, it could take days for the alarm to reach other settlements and for aid to come. If the city didn't have strong leadership, heavy fortifications, an effective army, and some sort of early warning system, it would quickly have been reduced to rubble. These towns and cities needed to be able to stand on their own, at least long enough for help to arrive.
This autonomy needs to be considered in fantasy cities, too. How does this autonomy look to your fantasy hero as they roam the streets? What sort of military presence does he/she see? What sort of early warning systems are visible – lookouts on towers? Beacons? Riders clopping through the streets carrying news from the outer garrisons? On a slightly more abstract level, how does this autonomy look in the eyes of the occupants of the city? Do they revere the lord of the city more than the lord of the land? Do they identify themselves as citizens of the Kingdom/Empire or as citizens of the city? Where are their loyalties, their frustrations?
I could go on forever, but I think I’ve made the point.
It might seem insignificant for the author to know what’s in an unadorned box on a desk in a minor official’s office – a box that plays no part in the story and is only mentioned once in a brief description. But nothing could be further from the truth. In fantasy, as in real-life, details do not stand in isolation. Stating a fact – whether it be the contents of a box, what someone is eating for dinner, even the colour of their shirt – opens up a wider net of links and facts that must be explored and explained. It’s this coherence that gives a fantasy world depth and realism, and makes it the type of place that could function completely if it were ripped from the pages and transplanted into some lonely corner of the real world.
Time to look again at our writing. Any boxes left unopened?