Hydrographer

Someone who makes nautical charts.

“When the Board of Longitude disbanded in 1828, at the repeal of the prevailing Longitude Act, its chief duty, ironically enough, had become the supervision of testing and assigning chronometers to ships of the Royal Navy. In 1829, the navy’s own hydrographer (chief chartmaker) took over the responsibility. This was a big job, as it included seeing to the rate setting of new machines and the repair of old ones, as well as the delicate transportation of the chronometers over land, from factory to seaport and back again.”

Dava Sobel, Longitude (1995).