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. And how troublesome the moon is! I have come to grief over the moon in Prince Otto, and so soon as that was pointed out to me, adopted a precaution which I recommend to other men — I never write now without an almanack. With an almanack, and the map of the country, and the plan of every house, either actually plotted on paper or already and immediately apprehended in the mind, a man may hope to avoid some of the grossest possible blunders. With the map before him, he will scarce allow the sun to set in the east, as it does in The Antiquary. With the almanack at hand, he will scarce allow two horsemen, journeying on the most urgent affair, to employ six days, from three of the Monday morning till late in the Saturday night, upon a journey of, say, ninety or a hundred miles, and before the week is out, and still on the same nags, to cover fifty in one day, as may be read at length in the inimitable novel of Rob Roy. And it is certainly well, though far from necessary, to avoid such ' croppers.'

Robert Louis Stevenson in an article My First Book - Treasure Island, which first appeared in McClure's Magazine in 1894