'Topos' were the mapmakers/cartographers of the engineer branch. Marshal Berthier and his father were both topographical engineers as was Bacler d'Albe.
The French ingenieurs geographes, usually mistranslated as 'geographical engineers' instead of the military term in English topographical engineers. They were first established in 1771 as the army's surveyors and cartographers. They were 'suppressed' by the National Assembly in 1791 and during the first years of the Empire they were assigned to the Depot of Military Archives but in January 1809 Napoleon resurrected them as part of the engineer arm as the Corps Imperiale des Ingenieurs Geographes.
This organization was composed only of officers, having 90 in the corps from sous-lieutenant to colonel. Their replacements were taken from the Ecole Polytechnique. Their facing color was aurore, in contrast to the black velvet of the engineer officers.
The corresponding naval organization was the ingenieurs hydrographes who were responsible for making the navy's navigational charts.