I believe that when I started at Heathrow (Jan '72) the maps were produced by some sort of scanning device and the maps were etched on to glass slides. This accounted for the ease which Tels were able to display Christmas trees on the radars on 25 Dec!
The maps were drawn in fairly large scale with a fine draughting pen, black ink on white cartridge, which was then photographed. The resultant
negative transparency (about 3" square if I remember rightly, but stand to be corrected) was then inserted in a glass mount, rather like an old-fashioned magic lantern slide, through which a trace on a separate CRT illuminated it in synchronisation with the revolving trace of the radar display. Which is why when the displayed scale was expanded, the map information became somewhat fuzzy and even kinked as the film distorted. However, the ACR430 did not even have this luxury - see separate thread.
2 s