Some NWI maps were produced using 1972-73 Mark Hurd
color infrared (CIR) prints at 1:80000. In the mid 1980s
NWI used aerial photos of 1:58000 scale, CIR transparencies,
flown between 1984-86 as part of the National High Altitude
Aerial Photography Project.
Source dates: 1970s & 1980s