Which Valais catchments have I never crossed on foot? I asked an AI agent to compare 998 walks and hikes with federal catchment data. First answer: precise—and wrong. After checking the inputs, the result moved from 17 to 60 of 135 catchments visited. The article shows the STAC, GDAL, SQLite, Shapely and PyQGIS calls behind the analysis—and why verification matters. https://digitalpathlines.ch/2026/08/31/which-valais-catchments-have-i-never-crossed-on-foot/ #GIS #OpenSource #AI #Valais