Grid - what grid? French maps aren't wrong, just real different from
how I'm used to
This might help other Brits make sense of French maps :)
You need a good map to find some of the more out-of-the way sites around Carnac. The map you need is the 0821 OT Top 25 map from IGN, titled Presq'île de Quiberon, Auray, Carnac. UK readers can get this from Stanford's above - select Topo maps, French TOP25 Serie Bleue. Completists might consider the 0921 OT Vannes/Golfe De Morbihan for the few stones around Locmariaquer but the few major sites on that sheet are easy to find from normal tourist maps. IGN maps have no ISBN number to locating them online isn't easy! Stanford's main store is in Long Acre, London and is well worth a visit if you're in the Covent Garden sometime - the cornucopia of maps of far-flung places all over the world is amazing.
Once you have this map you can then simply take it from there. The major and middling sites are clearly indicated on the map, so it is easy to locate them and visit them. However, I wanted to set myself some GPS waypoints and perhaps give map references, as I do for UK sites The rest of this page describes the messy way IGN France has implemented their map references, which complicates that process horrendously. If you aren't going to use GPS or the map references that's all you need to know - step right back to the Carnac page.
Menhirs aren't in the
habit of moving much, so finding them shouldn't really be a problem...right? My location
device of choice is the GPS, and this comes with inbuilt mapping so there's no problem
there, in principle. All electronic mapping seems to come from a common base, and in
practice coverage of the USA is great, and coverage of the UK is pretty good if you pay
the premium to get mapping which came from the Ordnance Survey. I can expect every road
apart from the tiniest cul-de-sacs to be on my Garmin Metroguide maps.
So my expectation of GPS mapping was of
the same for France. Take a look on the left, and compare it with the section of the
French IGN map below. It's basically worthless - 90% of the minor roads are missing. This
is typical of the sort of detail from Internet sources - see Mapblast's
version of the same thing which is equally undetailed. On the right is what a Garmin EMAP
shows when loaded with the Europe detailed map, showing it appears to be derived from the
same source. We're not really going anywhere fast with this. Our prehistoric ancestors
weren't good enough to put their stones near the sort of main highways shown on electronic
mapping. Well, okay, maybe stones didn't figure big in the highway designers mind. Which
is no bad thing, when one recalls the poor setting of Stonehenge
at the confluence of the A303 and A344. Remote and out of the way is fine by me with
menhirs, but it means that I need more detail. Lots more detail.
Enter the Institute Géographique
Nationale or IGN for short. IGN is the French national mapping agency, and their
1:25000 TOP 25 series just fits the bill here - you need the 0821 OT Presqu'Île de
Quiberon for most of the area around Carnac and the 0921 OT Vannes/Golfe De Morbihan for a
small bit covering the Locmariaquer section (the sites there are easy to find so you
don't really need that map...). Suitable maps were procured and I anticipated an easy hour
or so entering the grid references of the sites to load up my GPS after transforming the
coordinates in a similar way to changing the OS national grid references.
Whoa - hold that right there. Observe the section of map on the right. Fantastic detail - can't argue with that. But see those small black crosses which form the grid? Shurely shome mishtake here - why are they at such an angle to the scan! I assure you that the scan is within half a degree of the vertical edge of the map, and I kid you not - the grid on French maps is not aligned with the map edge. The good news is that the maps are aligned to the lines of longitude (ie true North up, give or take a tiny error from the map projection).
However, latitude and longitude are always the devil's own job to read off maps. For a start one degree latitude isn't the same distance on the ground as one degree longitude unless you're at the equator rather than 47º North, and the degrees are spaced widely on the scale, making interpolation difficult. Which is why we have national grid references, normally spaced equally at 1km intervals like the British, and Irish National Grids. That way one can read the position easily from the map, and the computer can do the grunt work of transforming the grid references to latitude and longitude. Which is why I go OS grid reference to capture locations with UK maps and let the computer sort it all out later.
Well, finding small things like menhirs in France from maps is a challenge. Let me refer you to IGN's own web site FAQ, where obviously Frenchmen (or in this case -women) are also at a loss to how the heck you take a grid reference from a French IGN map and it's skewed grid. It's a messy process involving long rulers and acrobatics.
To compound the problem, there is also the little issue of national pride. An international conference in 1884 established Greenwich as the 0° longitude datum, instead of Paris, which lies 2º 9'22" east of Greenwich.
So the map scale gets cluttered with
extraneous rubbish. Nobody really cares how far west of the Paris meridian the longitude
is, but the main black lines of map are at tenths of degrees relative to Paris. The
position relative to the Greenwich meridian that GPS, and indeed everybody else uses is
relegated to tick-marks on the edge.
Hot tip for users wanting to issue a French Grid reference on one of these maps - just use the blue numbers, and tally them with the skewed grid. Then use something like the Java applet provided by these nice people to transform the coordinates to Latitude and longitude if that's what you want to do. Note that if you issue the grid reference in Lambert coordinates you must specify the Lambert zone used on the map (for Carnac it will be zone 2) just to add a little extra unnecessary complication to your life. One has to ask how it was that the Ordnance Survey, dealing with a country about 1100km tall (from Land's End to the Shetland Islands) managed to do the job with a single scale, whereas France, dealing with a country that was about 1000 km high needed no less than three difference coordinate transformations and still neeeded to treat Corsica separately. Corsica extends the total span of the grid to 1500 km N-S, but since it is an island treated separately in the existing grid, one would have thought that there could be one Lambert scale covering the entirety of France mainland.
So there you have it. It's no fun at all extracting map references from French maps, compared with the delightful simplicity of the process on British and Irish maps. But it can be done.
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