Monday, 28 December 2009

The Cassini Maps (updated)

When we unearthed the colombage wall of the lounge with its mud torchis, I wondered if that was an indication of the age of the house.  Did mud filling between the wooden beams come before brick?Unfortunately it's not that simple. The filling used depended partly on what was available and also the wealth of the owner.

I went to our local mairie to see if they had any information, but all they could suggest was to look at the Napoleonic maps.  Drawn up in the mid-nineteenth century, the maps were for tax purposes and certainly are an amazingly detailed record of the period.  Every field and building is marked and numbered.  However I was looking for something earlier.  And I found it in the Cassini maps.

Italian-born Giovanni Domenico Cassini moved to France in 1669 and became astronomer/astrologer to the Sun King Louis XIV.  He developed a method of measuring longitude based on an approach suggested by Galileo and started to map the topology of France in the 1670s using Gemma Frisius's technique of triangulation.  Through the following century the work was continued by his son, grandson and great grandson to produce a total of 180 maps covering the whole of France.

The maps are available on-line in several places, but the source I find the most useful, because of the quality of the reproduction, is  Finding our small part of France was a challenge as the mapping does not follow a logical sequence.  So the map for the environs of Agen was published in 1778, whereas our neighbouring map of what is largely now known as the Lot and Garonne was not published until 1783.

I was not sure I would find us. but I think we are there.  Although our lieu-dit is not named that of our neighbour is and a house stands on what looks to be our outcrop.  Two streams run down to the river in the valley below.  Where those streams were we are now bounded by ditches.  Given that the land was being mapped over many years, we now have a pretty good idea that our house is at least 220-230 years old.

The maps are wonderful in their topographical detail, we can see the walls of bastides, chateaux, churches, windmills, barns, woods, streams, the shapes of hillsides and valleys.  We can see the lack of roads and how in most places around here people would have crossed fields to reach their destinations.  There are only one or two bridges that cross the Garonne and the Lot, so crossing would have been by ford or ferry.


I've been asked for a legend for the maps.  Again there are several sources, some more complete than others. The best I've found (in colour) is on the website. On their navigation page, under the map of France, on the left hand side, there is an L in a circle. Click on this and a new page opens up with an excellent index of all the symbols.

Link to this page:  : cassini maps in colour.   Click on the L in the circle on the lefthand side under the map for a very detailed legend

Other links:
Giovanni Domenico Cassini  historic maps from all over the world
Geoportail:  another source for the Cassini maps : a useful link to a short version of the maps' legend


  1. How amazing to find those maps!
    I am going to follow that link to see what the world was like in this part of France!