roduct, far more accurate and detailed than any previous maps. They were published from 1798 through 1812. Reproductions of these maps are available for all of France from the Institut Geographique National in Paris.
These historic maps are extremely detailed and spatially accurate, much more so than the older Sanson map we possess created 100 years before. The Cassini maps provide us with the oldest, detailed, reasonably accurate record of the location of roads, bridges, towns, streams, and villages of the area. It also shows information about the current vegetation and land-cover of the area. The maps contain an astounding level of detail. This is a particularly fortunate period for obtaining accurate cartography of the region, as it is before the French Revolution. The map scale of is 1:86,400.
The map scale that was used for these maps then was in the old units of measurement:
1 ligne=100 toise.
One toise (English fathom) was equal to 6 pieds (English feet), one pied (English foot) was equal to 12 pouces (English inches), and one pouce was equal to 12 lignes (English lines). So one ligne (1/12 of an inch) on the map was equal to 100 fathoms (600 feet) on the ground...thus a modern scale, or more properly, the repesentative fraction, of these maps is 1:86,400 (or 1 : 6x12x12x100).
A 'toise' was a traditional French unit of distance comparable to the British fathom (or 6 feet). Like the fathom, the toise originally represented the distance between the fingertips of a man with outstretched arms. Introduced by Charlemagne in 790, the toise is such an ancient unit that the French 'toiser' has become a verb meaning "to measure" or "to size up."
The toise equals six pieds (French feet). The 'pied' was the traditional French foot. Pieds of various lengths were used in France, but the one best remembered now is the royal foot (pied de roi), called the Paris foot in English and the foot (French measure) in Canadian law. The pied de roi equals about 32.48 centimeters or 12.79 inches; the official Canadian definition is 12.789 inches (32.484 06 centimeters). Today the word pied is sometimes used informally in France as a metric unit equal to 30 centimeters.
The 'pouce' was the French "inch" unit, equal to 1/12 pied. Based on the pied de roi, the pouce equals about 1.066 inches or 2.707 centimeters. The word pouce actually means "thumb" in French.
The 'ligne' was the next smallest traditional unit of distance in French speaking countries, equal to 1/12 pouce (French inch) and corresponding closely to the English 'line'. The Swiss ligne is still used throughout the world by watchmakers; it equals about 2.256 millimeters (0.0888 inch) and is further divided into 12 douzièmes.
So...1 ligne=100 toise equals 1:84,600. Simple!
Source used on measurements: "How Many? A Dictionary of Units of Measurement" © 2001 by Russ Rowlett and the University of North Carolina at Chapel Hill. http://www.unc.edu/~rowlett/units/index.html
1759 Cassini Map of the Mt. Dardon area
This section of the Cassini map clearly shows the extraordinary amount of detail and useful data contained in these documents. The map is centered on Mt. Dardon, with the village of Uxeau to the Southwest. You can clearly see the general topography, roads, individual structures, and many water mills and mill dams. The key for the different map features is below. You can see that each type of structure is identified, as are different types of bridges, mills, and vegetation zones. The walled city of Issy L'Eveque is shown in the upper left, and the number of mill ponds and grain mills in the region is amazing. Few of these remain intact today. Research on the information contained in these maps is ongoing.
1759 Cassini Map key
Portions of the Cassini map, showing Mt. Dardon and Toulon. On the left you can see some of the many mill ponds and dams found throughout the region in the 1700s. Most of these are now gone. Click on the map at right to see some analysis that used this map.
1759 Cassini Map Digitization
Rutgers Graduate Student Bob Wiencek digitizing mylars from the Cassini 