This month the main mapping work completed has been in Volume 1 where the maps of the Donnellys Crossing or Kaihu Branch have been updated. This has been undertaken with assistance from members of the NZ Rail Geography Group on groups.io which is likely to be significantly beneficial to the rest of the project as well. Apart from this section of Volume 1, a lot of work has gone into preparing the annual aerial survey request from Linz and this year the request will be for 93 individual surveys covering Volumes 4, 7, part of Volume 6 and part of Volume 1. The request is expected to total up to 2 TB of data because in order to reduce the work needing to be done by Linz staff, generally the requests are for whole surveys regardless of the amount of coverage needed. It is only in the case of a handful of these 93 surveys that the request would be for a specific range of photos from the survey; apart from making it quicker to receive the request it also reduces the amount of work the Project has to do to decide which specific aerial photos cover a particular area, which can be difficult because the footprint boundaries that are shown in the aerial surveys data layer from Linz are not always particularly accurate. The preparation of the request will be completed by the end of this week and it should be received within a couple of weeks. It has been necessary to add 3 TB of additional disk storage to a Project computer to store these aerial surveys whilst they are checked for the appropriate content and it goes without saying that this disk space will all need to be freed up by the time of the next annual request, so it is the case that the volumes that these aerial surveys are linked to are likely to be those most progressed during 2025.

The other significant work progressed this month has been in preparing to update the web maps. This requires that the web map tiles first be generated for the existing maps (what is currently displayed on the website) and then the new format generated over the top of them. Essentially because the volume boundaries and most of the data table formats were changed since the last update, the GIS project file that generates the web map tiles has to be changed to use the new data tables and the extents files for each volume have to be updated with the new boundaries. The web map tiles are generated in one base layer and six overlay layers, which are user selectable in the web browser – the base is always turned on and can be selected between the project’s topographic layer and the Linz Base Map online layer, while the user can select from 0 to 6 overlays to be displayed at any time. The GIS project needed to generate these groups of tiles is much complicated than the projects used to edit the maps because the source data layers are generally spread across the seven tile groups multiple times each with just a part of each layer’s data in each of the groups it belongs to, as the way the data is structured for the web maps is quite different from the way it is structured in the GIS.

So the first stage of the update will commence with Volume 1 rather than Volume 6 as previously suggested and the update capture should be completed within the next 1-2 weeks so that the update will be available next month. Provision was previously made for historical aerial photos used to create the maps to be included with the web maps in decades and displayed on the website. To date only a small part of Christchurch actually has any historical aerials displayed on the website but some effort will be made to evaluate this further to see if it should be worthwhile adding comprehensive historical aerial coverage to the website all across NZ. The main issue is the amount of storage required on the web server for the aerial layers and this will be evaluated as part of the decision process about this feature.