In accordance with the intention to develop all volumes this year, I am starting work on creating Volumes 1 and 2 today. Volume 1 covers the North Auckland Line and its branches, which is everything past Newmarket in Auckland. This means basically all the railways in Northland.
Volume 2 is the North Island Main Trunk, which is from Wellington to Auckland. This includes the railways in Wellington, Palmerston North, Hamilton, Auckland and a number of other centres. The NIMT part is needed to finish Volume 4 where the SOL joins onto the NIMT.
I am currently downloading Auckland City aerial photography from 2017 at 0.075 metre resolution. This will take around 40 GB of downloaded imagery but the amount actually needed to cover the rail network of Auckland will be considerably less. At this resolution it is only for modern coverage. Anything that is an aerial mosaic should use the separately downloaded older 0.125 resolution coverage to reduce the number of tiles needed to cover a station area. However no mosaics are planned but I may do one of Auckland's Strand station sometime soon, especially if there is official NZR survey coverage for it. Likewise I may do one of Frankton and/or Te Rapa. I have already done a number of Wellington so these can be added in to the Volume 2 stuff. PN is not possible as no Retrolens images have yet been released for Horizons RC. The rest of the NIMT will undoubtedly be lower resolution probably 0.3 to 0.4 metres. Although Volume 2 was created last year I have only done a bit of Wellington so far.
It would have been interesting to have had georeferenced aerial photography of Auckland from mid 2000s for comparison of the double tracking and other improvements but that isn't possible unfortunately.
Northland coverage comes to 0.4 metres dated 2014-16 for the whole region as well as some 0.1 metres of a few small areas. The 0.4 stuff will be adequate but does not really have the sharpness needed for tracing the current rail lines. It's a pity they do not have 0.3 metres but I guess that is the reality of a less populated area. The 0.1 stuff should cover Whangarei and one or two other urban areas well enough.