Draftsman and cartographers would have worked on these maps on some kind of parchment to enable tracing. If they were quite technologically advanced, they probably worked on overlays; a layer for the physical features; a layer for the man-made features; and a layer for the lettering. (Or some variation upon that.)
They no doubt used some kind of architectural scale to make distances on the ground easily transferable to the paper. They would have used india inks of different colors, and a dozen or so pens with different sized metal nibs. They probably would have penciled in rough reference lines and later erased them. These cartographers would have been proficient in hand lettering, an all but lost art today. Those old artisans would have had years of practice doing cross-hatching with a triangle and pen. Line after parallel line, one after the other. They would have to be quite artistic to do the squiggles showing the hills and berms. On the map they resemble thumbprints. And there are stipple patterns too. They would have used French Curves to make nice smooth curved lines, and used compasses for the circles and semi-circles.
Coastlines are shown by a series of lines mimicking each other, each additional one softer until they become quite smooth and flowing. Freehand or with French Curves, I can’t tell.
Needless to say, I’m blown away by the artistic beauty of these maps. You can appreciate them on several different levels. One; they do a good job of showing what’s on the ground and help you find your way around, which is all they are really supposed to do. Two; they were works of art, and even if they were not useful, functional maps, they would be beautiful things to look at. And three; you have to respect the sheer amount of tedious work that went into these maps. It must have be tiresome to take all the measurements and transfer them onto rough drawings in the field. Tiresome to convert the rough drawings and measurements to a scaled down, rough map. And tedious to take the rough map and convert it to a beautiful, understandable, functional map.
Today, aerial and satellite photos, computers, computerized drawing programs do all the work. I sincerely doubt that anyone goes into the field and takes measurements with a measuring tape. No one sets india ink on paper with a slotted nib anymore. Today, no one hand letters "Ocean Atlantique" in such a beautiful manner.