A-Z ‘phantoms’ had already been added to maps in order to identify unauthorised copying. However, the increasing availability of drum scanners in the early 1990’s raised concerns that a map could be quickly reproduced in this way and printed without the copyright owner’s permission. Stephen Dobson, a copyright solicitor, suggested placing an arrangement of dots (‘Dobson dots’) on the map as a solution. This idea was adopted for the Greater London area and was set out across the 9 Sheet Master Map series. The diagram here shows that by putting the 9 sheets together and joining up the dots the AZ logo is revealed. The lines drawn on the north 9 sheet behind show the relevant section of logo.