The Cassini Map of France

Section from Cassini Map

Have you ever heard of the Cassini Map? This is the first comprehensive, detailed map of France, compiled following survey work carried out between the 1740s and 1780s. You might well find your house or hamlet on it – it’s as detailed as that.

I was already aware of the map, having read Graham Robb’s social history of rural France, The Discovery of France (Picador, 2008, ISBN 978-0-330-42761-6). He mentions it, and the work behind it, in several places. However, it was only recently, on hearing someone else mention it, that I decided to find out more about it and see if I could find it on the Internet.

The inspiration behind the map was a character called César-François Cassini (known as Cassini III), who came from a line of geographers/explorers. Born in 1714, he died in 1784 before all the sections of the map were published (it took until 1815 for it to be published in its entirety). His son, Cassini IV, took over the work and oversaw its completion.

Cassini had three ambitious objectives in embarking on this stupendous task:

  • “To measure distances by triangulation and thus establish the exact position of the settlements;
  • To measure the Kingdom, that is to determine the innumerable number of boroughs, towns and villages scattered throughout its territory;
  • To represent that which is unchangeable in the landscape.”

This was no mean feat in a country which was less than centralised, where the transport system was primitive and the road network minimal and where the locals were often hostile, not to say downright dangerous. Graham Robb recounts in his book the fate that befell one of Cassini’s young surveyors who ventured into the Cevennes in 1740 and was hacked to death by suspicious natives. Elsewhere, the surveyors came across resistance from people who thought this was an ill-concealed plot to raise taxes or who simply did not like external interference.

The financing of the work was by no means certain, either. To start with, owing to Louis XV’s interest in the project, Cassini received grants from the Treasury. However, when the Seven Years’ War started in 1756, financial support was withdrawn and Cassini had to start a subscription offer to finish the project.

Cassini’s team managed somehow to surmount all these obstacles and the result was the first fully comprehensive mapping of the territory of France. Some 188 sheets were produced, showing not only place names and roads but also topographical features such as rivers and escarpments. The position of some of the places is not always completely correct – no doubt the surveyors got cheesed off with being shot at and simply made a guess in some cases. But, apparently, if the Cassini map is superimposed on the current map of France, the road network (such as it was then) follows remarkably accurately the line of today’s roads.

After some trial and error, I managed to find our place on the map via the Internet. As far as I can tell, we are on the Montauban sheet, which was surveyed in 1771-72 and published around 1777. Most of the place names have survived intact, although the spellings are sometimes different. A few places appear to have had completely different names, which have been superseded by a modern spelling.

What it shows is that our area was comparatively densely populated before the French Revolution. We already knew that the population of our commune in 1900 was about 4,000; by 2000, it had fallen to around 1,200. However, I had thought that many of the hamlets were established in the 19th century. Now I know they are older than that.

I have spent several hours poring over the small section of the map on which our lieu-dit (or hamlet) is marked (I know, I should get out more). I find it absolutely fascinating. I would love to know what it looked like at that time, who lived here and what their stories were. Unfortunately, records from before the Revolution are sparse and not always reliable. The Cassini Map is therefore a very valuable document in showing where the settlements existed.

If you are interested, there are several ways of finding the map on the Internet:

  • Type Cassini Map, or Carte de Cassini, into a search engine.
  • Go to the gencom website (click here) and enter the name of a lieu-dit, hamlet or village. This takes you to a list of documents that include that name, including the Cassini Map. Click on Cassini Map and it should bring up the sheet you’re looking for. Not all the place names are indexed (ours wasn’t) so you just have to keep trying with place names close by till you get there.
  • Go to the ehess website (click here) where you can click on a map of France and get progressively down to the area you’re interested in. It took me a while to work this site out but it worked OK once I did.

I intend to find out more about the making of the map and will report later on anything I think might interest people.

P.S. If you find any sites featuring the Cassini Map that are more user-friendly than the two listed above, please let me know. They are not the easiest to get to grips with.  See Janice’s comment below about geoportail[dot]fr, where you can superimpose the Cassini map on the current map of France showing where you live and see how it compares.

Copyright © 2010 A writer’s lot in France, all rights reserved


  1. lets you choose to superimpose the Carte Cassini on today’s map of where you live. Fascinating. Just enter the name of your commune and then open the folder Cartes. You can alter the opacity to show views simultaneously. You can also get cadastre information from this site.

    Have fun.


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