Britain from above is a new online service, cataloging photos from the early part of the 20th century, taken from the air. So far i have only found pictures taken of London and the now closed Belle Vue zoo, Manchester. http://www.britainfromabove.org.uk/asearch?search=zoo http://www.britainfromabove.org.uk/asearch?search=zoological More photos will be added to this invaluable online library in due course.