The published maps of Middle-earth by Christopher Tolkien drew on extensive drafts made by his father during the process of his writing. These drafts enable tracing the possible influence of the elder Tolkien’s training in map-reading during his time in the British Army during the First World War. The early maps drawn by J.R.R. Tolkien exhibit features, such as the use of hachures and contour lines to indicate elevation, and a focus on the accurate calculation of distances and movements, that were characteristic of military cartography. The maps then evolved into a more pictorial style, characteristic of contemporary literary maps, as they were prepared by Christopher for publication.
"Military Cartography’s Influence on Tolkien’s Maps of Middle-earth,"
Journal of Tolkien Research: Vol. 11
, Article 1.
Available at: https://scholar.valpo.edu/journaloftolkienresearch/vol11/iss2/1