During the Cold War, the Soviet military mapped the entire world, parts of it down to the level of individual buildings. The Soviet maps of US and European cities have details that aren’t on domestic maps made around the same time, things like the precise width of roads, the load-bearing capacity of bridges, and the types of factories. They’re the kinds of things that would come in handy if you’re planning a tank invasion. Or an occupation. Things that would be virtually impossible to find out without eyes on the ground.