One map which is depicted in many books on the history of Thailand is titled "Carte du Royaume de Siam et des Pays Circonvoisins" (Map of the kingdom of Siam and surrounding countries). This map was drawn by R. Placide Augustin Dechaussé, royal geographer of the French King Louis XIV. It was drawn in 1686 in dedication to the voyage of Alexandre de Chaumont to Siam as the first French ambassador. It's a pity I don't speak French, as the website Mémoires de Siam not only present the manuscript of de Chaumont (which is available in an English translation from Silkworm Books), but also other texts which seem to have no currently available English version.
Another great online essay which mentions this specific map is The Mapping of Thailand: An Introduction by Dawn F. Rooney. Yet what is really sad - even though this map is long in the Public Domain, there seem to be no high-quality scan available online which would allow to print it in its original size of 33.5 x 47.0 cm. In most books the map is depicted in black-and-white, yet it was beautifully colored. The best online resource showing the whole map seem to be the map collection of the Chao Phraya Delta Research website, thus I used that version to show in this posting. NDMI-Oldmap is another collection of old maps, which has two larger scans of this map, but both a bit blurred. The one on Wikimedia Commons is simply awful.