1. Josef Konvitz, Cartography in France, 1660-1848: Science, Engineering, and Statecraft (Chicago: Univ. Chicago Press, 1987), pp.67-70, specifically argues that Cruquius's map predates French maps with depth lines. See also
2. Van den Brink, "Ineen opslag van het oog"), pp.58-60;
3. Chasing the line: Hutton’s contribution to the invention of contours