In answer to your question, Jean.
They used the detailed Ordnance Survey 6" maps printed in the 1930s and aerial reconnaissance flights of the UK, which began before the start of, and during the war, for use in their planned invasion of England in 1940 - Operation Sealion. Their spying operations in the UK weren't very successful.
They also used tour guides and postcards of the UK.
After the war, the British found 16 tonnes of aerial photographs of the UK and Europe, which became de-classified in 1974.
RAF Port Ellen (Coastal Command) 1941
German aerial photograph
Operation Sealion 1940