Wednesday 8 January 2020

Palmerston North Gisborne Line [0I]: Volume 5 Progress Update 9

In addition to the production of the maps themselves, a lot of changes have been made to the amount of detail displayed particularly on the aerial maps and in terms of generations of aerial maps.

For certain areas we have chosen to produce multiple generations of historical map tiles. This means that some of the features we trace will be only present in some generations and not others. We did implement and design a system to enable the features to be filtered according to the generation they appeared in. Whilst this is not difficult to operate, it adds complexity when outputting the different map generations.

We decided therefore that in order to make it simpler to output multiple generations of maps without having to filter features according to each generation, apart from having to identify the generation features belong to, we would simply digitise and display all the features across multiple generations in one diagram.

We also decided that we would remove buildings, structures, sites and voids from aerial maps and this information would only be displayed in diagram maps. This would reduce visual clutter on aerial maps and also simplify the production of them.

All aerial maps will therefore be limited to displaying the following layers:
  • Locations (Stations, milepegs etc)
  • Bridges and Tunnels
  • Features
  • Main lines (current or former)
  • Roads will only be indicated by captions, not actual lines showing their route, on aerial map
  • Aerial photography background

Diagram maps will display the following layers:
  • Locations (as above)
  • Bridges and Tunnels
  • Features
  • Main lines (current or former)
  • Road routes and names
  • Footpaths, vehicle tracks etc
  • Ropeways, tramways,  pipelines, miniature railways
  • Yard tracks
  • Buildings
  • Structures
  • Sites
  • Voids
  • Property boundaries
  • Contour lines
  •  Spot elevations
  • Place names
  • Rivers
  • Lakes
  • Streams
  • Terrain relief background images
 As you can see there is a lot more information in a diagram but it is much less likely to clash with the background. The terrain relief images are a very light grey in colour for the most part and do not visually interfere with the other information displayed as tends to happen with aerial photos. There are also not the issues of features that have been digitised on a map covering up parts of an aerial photo.
The new styling will take effect with the production of the Wairoa and later sections of the PNGL main line corridor but at some point will be retroactively applied to earlier parts of the corridor that have been produced to date, once we have had time to bed in these changes.
As noted previously a lot of this change is because of the now widespread use of aerial photography in the maps, whereby it has become desirable to determine what is the best way of combining aerial photo backgrounds with the existing information in a map, most of which works well on a diagram format but creates various challenges with an aerial photo background.
Below are maps of Wairoa created under the new changes. In our last post we produced 16 maps of Napier out of a total of 24. Given that the maps of Napier covered a total of four actual areas, under the new styling rules, for each area we would have produced the 1973, current and diagram maps, which would have resulted in 12 maps instead of 24.
The historical of Wairoa below are aerials for 1942, 1962, 1970, 1979 and current, followed by the diagram. Hopefully this makes the effect of these changes clear enough.