German espionage in pre-Occupation Paris

May 2019
Paris, France
When German troops occupied Paris in 1940, they requisitioned the buildings they needed (hotels, offices, etc) so quickly that they must have staked them out in advance. But how did they do this? Spies acting as tourists? Detailed studies of guidebooks? Other methods? Are there any books or articles (in English, German or French) that outline these preparations? Many thanks!