I am mountaineer from many years ago so that I know very well mountain areas in Pyrenees in the border between France and Spain.
Now when beginning to upload some of my gps mountain tracks I have seen that the border is wrong by kilometers :(.
I have checked that the “source” tag has “CIA World Databank II”.
Using OSM Yahoo satellite images and supported by my gps data I feel able to fix kilometers of border with a 100-50 m precision. This is possible thanks to the border crosses by mountain peaks easily viewed in the least that perfect Yahoo images.
Until now I have uploaded roads streets, parks, …, but never borders between countries!.
It is strange for me but I think I can do it reliably.
Thank you for your help. I have posted it in users:France.
Anyway, I have done a test. I have drafted about 30 km of the border in central Pyrenees high altitude area using the method posted before and I have compared it against different sources. One thing to remember is that in this area the border goes closely related to geographical features specially peaks, ridges, crests and mountain passes over 2000 meters altitude.
Spanish Government “Instituto Geografico Nacional (IGN-ES)”. Their border definition is the best as their maps define in addition every single geographical feature (with or without name) where the border passes.
French Government “Geoportail (French Institute Geographic National)”, including “Parcelles Cadastrales”
The results are in order from the best IGN-ES, Geoportail/Hand made, Google Maps.
Hand made system has similar quality to Geoportail Cadastral results as this one seems to have small mistakes (remember that the border goes by many places only accessible by climbing). Google Maps appears to be based in IGN-France data but with additional mistakes. In all of them the error is less than 100 meters, that for high mountain is not very bad.
The reason of the quality of hand made border is that Yahoo images seem to be geographically very well located and they have been taken with the sun in angle (not at noon) so that the crests and peaks are very clearly delimited.
“CIA World Databank II” data in this area is so poor that in kilometers distance it is at about 3 km from real border, so I think this should have to be fixed immediately.
I have checked more high mountain Central Pyrenees border and I have seen that French Cadastral data has relevant errors (around 200 m) in Vignemale area (alt. > 3000 m, Montferrat area). Here the border goes by an inaccessible precipice instead of by a well defined crest as indicated in various cartography sources I have.
The imported CIA World Databank borders are known to be of quite low accuracy - this is especially visible where the border follows some natural features, be it rivers or peaks and not just some artificial coordinate lines. Unless someone has imported borders converted straight from the local legislation or other official source from within the affected country, you can be quite certain that your measurements are better.
SIGPAC has excellent border maps that detail every geographical feature that detail the border (and much more), so it is easy to match Yahoo imagery with ground features, like mapping a town.
Initially I wanted to use very old books and maps to add “names” to the map, but as SIGPAC has so many information and OSM can use it, I will be much more productive, so it is not bad to add “Sigpac” in “source” tag.
In summary the idea I have is to add as source tag something like this: “Yahoo aerial imagery, Sigpac and personal experience”.