Here”s a bit of advice from Robert Louis Stevenson, in writing about the genesis of Treasure Island (from his 1905 short work Essays in the Art of Writing). He speaks to the imaginative power of starting by making a map!
The story begins in 1881 in the Scottish Highlands, during a rainy spell spent confined in a cottage, as Stevenson spends time fooling around with watercolors with his stepson.
There it blew a good deal and rained in a proportion; my native air was more unkind than man’s ingratitude, and I must consent to pass a good deal of my time between four walls in a house lugubriously known as the Late Miss McGregor’s Cottage. (. . .) There was a schoolboy in the Late Miss McGregor’s Cottage, home from the holidays, and much in want of ‘something craggy to break his mind upon.’ He had no thought of literature; it was the art of Raphael that received his fleeting suffrages; and with the aid of pen and ink and a shilling box of water colours, he had soon turned one of the rooms into a picture gallery. (. . .) I would sometimes unbend a little, join the artist (so to speak) at the easel, and pass the afternoon with him in a generous emulation, making coloured drawings.
On one of these occasions, I made the map of an island; it was elaborately and (I thought) beautifully coloured; the shape of it took my fancy beyond expression; it contained harbours that pleased me like sonnets; and with the unconsciousness of the predestined, I ticketed my performance ‘Treasure Island.’
I am told there are people who do not care for maps, and find it hard to believe. The names, the shapes of the woodlands, the courses of the roads and rivers, the prehistoric footsteps of man still distinctly traceable up hill and down dale, the mills and the ruins, the ponds and the ferries, perhaps the STANDING STONE or the DRUIDIC CIRCLE on the heath; here is an inexhaustible fund of interest for any man with eyes to see or twopence-worth of imagination to understand with! No child but must remember laying his head in the grass, staring into the infinitesimal forest and seeing it grow populous with fairy armies.
(. . .) Somewhat in this way, as I paused upon my map of ‘Treasure Island,’ the future character of the book began to appear there visibly among imaginary woods; and their brown faces and bright weapons peeped out upon me from unexpected quarters, as they passed to and fro, fighting and hunting treasure, on these few square inches of a flat projection.
The next thing I knew I had some papers before me and was writing out a list of chapters.
(. . .) Fifteen days I stuck to it, and turned out fifteen chapters; and then, in the early paragraphs of the sixteenth, ignominiously lost hold. My mouth was empty; there was not one word of TREASURE ISLAND in my bosom; (. . .) I was indeed very close on despair; but I shut my mouth hard, and [a bit later] down I sat one morning to the unfinished tale; and behold! it flowed from me like small talk; and in a second tide of delighted industry, and again at a rate of a chapter a day, I finished TREASURE ISLAND.
(. . .) I had written it up to the map. The map was the chief part of my plot. For instance, I had called an islet ‘Skeleton Island,’ not knowing what I meant, seeking only for the immediate picturesque, and it was to justify this name that I broke into the gallery of Mr. [Edgar Allan] Poe and stole Flint’s pointer. And in the same way, it was because I had made two harbours that the HISPANIOLA was sent on her wanderings with Israel Hands.
(. . .) I have said the map was the most of the plot. I might almost say it was the whole. A few reminiscences of Poe, Defoe, and Washington Irving, a copy of Johnson’s BUCCANEERS, the name of the Dead Man’s Chest from Kingsley’s AT LAST, some recollections of canoeing on the high seas, and the map itself, with its infinite, eloquent suggestion, made up the whole of my materials. It is, perhaps, not often that a map figures so largely in a tale, yet it is always important. The author must know his countryside, whether real or imaginary, like his hand; the distances, the points of the compass, the place of the sun’s rising, the behaviour of the moon, should all be beyond cavil.
(. . .) But it is my contention – my superstition, if you like – that who is faithful to his map, and consults it, and draws from it his inspiration, daily and hourly, gains positive support. . . . The tale has a root there; it grows in that soil; it has a spine of its own behind the words. Better if the country be real, and he has walked every foot of it and knows every milestone. But even with imaginary places, he will do well in the beginning to provide a map; as he studies it, relations will appear that he had not thought upon; he will discover obvious, though unsuspected, short-cuts and footprints for his messengers; and even when a map is not all the plot, as it was in TREASURE ISLAND, it will be found to be a mine of suggestion.
The take-away: draw a detailed map. You may be surprised what it adds to the richness of your story.