Hans - Karl,
It is my belief that few persons used the metric length measurements at all during the Napoleonic period, including the Emperor! They used the measurements that were familiar to them. I was trying to recall if I ever saw a distance measurement in meters, used in a memoire or document of the time - other than in scientific or engineering fields. I could not recall any.
It would be interesting to hear from other colleagues as to the use of metric measurement when determining distances during this period.