I have decided to add maps of Christchurch Station in 1940, 1950 and 1961 to the mosaics. This will be purely for comparison with present day purposes as these are not as high a resolution and it would be time consuming and difficult to trace the track layout. Also only the actual station yard will be covered as there have not been enough changes in the adjacent areas to justify the work needed to add the older aerial photos to the mosaics. (UPDATE: I also obtained 1984 and 1994 images and added them. The latest version of Gimp has the Unified Transformation tool which makes aligning aerial images really fast and meant each of the new images only took mere minutes to align to the 1970 aerials)
In the meantime I have begun drawing the track at the station and other details and here are a couple of comparison shots from 1970 and 2015.