After our last post about extra work being discovered as we got into more depth of working on lines in the Gisborne area, that trend has continued today. Whilst in the course of tidying up all the aerial photography around the Gisborne area and labelling many of the sidings off the main line, we discovered a second NZR aerial survey for Gisborne Station.
To explain this in more depth, Retrolens has many different survey sources, most of them various government departments. The ones that have consistently proved most useful for NZ Rail Maps are the highway surveys done by the Roads Board et al (where these highways are close to railway lines) and the ones that NZR themselves had done. Most of these are around 1:8000 in scale. Indeed, the aerial survey we used to map the Cromwell Gorge section of the OCB for Volume 12, dating from 1962, is a highway survey (SH8), as were some other historical surveys of the railway around the Clutha Valley.
NZR aerial surveys mainly take two forms. Major stations had their own surveys, which are generally carried out at a scale of about 1:4300, though there are a small number at a larger scale. Often there will be just one run (Run A), but occasionally with a big area, for example the Port of Lyttelton, with changes in direction, there can be several runs to get everything covered.
In addition, major rail corridors had corridor surveys, which are generally at a scale of 1:5500. They cover a whole corridor or part corridor using multiple runs because of the fact that no corridor runs in a straight line, but the aerial survey aircraft must fly in a straight line for each run. There are no corridor surveys for less important lines like the Hokitika/Ross branch, Otago Central Branch, Kingston Branch etc. They just cover the major corridors, which includes the Palmerston North Gisborne Line in this instance - the corridor survey around Gisborne was done in 1986 and happens to include the Makaraka Branch in the last run into Gisborne Station.
Going back to the station surveys, some stations had more than one done. When we first came to do Gisborne Station in 2018, the survey we found at that time was dated 1968. We do not recall if the 1982 survey was found at that time, but the 1968 one was chosen. Having done more investigation today into the area around Gisborne Station and the various private sidings, we are now creating map tiles for that era in Gisborne, which will add another era to the historical aerial maps, as well as giving more detail to add to the diagrams.
Today we also finished drawing the yard layout for Matawhero. This means the next part of the M-M-M series can be written tomorrow. Whilst looking in the area, we removed Gisborne Aerodrome as a station. This is shown in the Quail Atlas 4th edition, but Dates And Names suggests that it was for a siding that was never installed, so it never existed. We are fairly confident of having got everything we need for Gisborne now, and so there is just Muriwai Station to complete mapping the area and allow us to push on back towards Napier and points further south in finalising the maps to be completed next week.