Want to plan your NZ tramp using digital topographic maps? Like to view NZ Topo50 maps on your iPhone or Mac? What sorts of maps are best for tramping? How do you select the appropriate map? How can you load and calibrate these maps on an iPhone or Mac computer? What are some of the technical problems?
New Zealanders are certainly lucky to have high quality recent produced raster digital topographic maps (300dpi) available for download for FREE , and despite some controversy, the change to NZGD2000, which is equivalent to the universally used WGS84 for bushwalking purposes, has brought some bonuses for those of us who like to use NZ maps on our iPads and iPhones. There is no doubt that for tramping a 1:50K topographic map is needed and for steep terrain a 1:25K map is even better.
Many newer mapping programs that may not have been able to use the old NZGD1949 datum, but do have the newer WGS84 datum installed, are now able to be used by bushwalkers/trampers in NZ. Two of my favourite navigation apps, Bit Map for the iPhone and MacGPS Pro for the Mac computer can now view and use the latest NZ Topo50 (1:50K) and Topo250 (1:250K) maps. No doubt any GPS that is able to load non-proprietary maps will be able to used these maps too.
Land Information New Zealand (LINZ)
The new Topo50 and Topo250 map series are available for download from the Land Information New Zealand website in two formats
- geoTIFF (141 Mb for a typical map) (no map legend or margin, but includes embedded calibration data to allow automatic georeferencing and alignment of adjacent maps)
- TIFF (214Mb) (includes the legend and margins, identical to the paper version)
The first step is to decide which map you wish to download and this can be done by going to the LINZ Map Index page and selecting the appropriate 1:250,000 map. Once you have selected the correct large scale map, clicking the large grid square, will reveal twenty five, 20 km x 20km 1:50,000 maps which can then be individually selected for download.
Loading Topo Maps into your Map Viewing App
Bit Map requires that you first convert the geoTIFF map image file ( no margins or legend) into a form that it can read and labels .bitmap. This can be done within your iPhone or using a desktop application, such as those available free of charge on the developers website, which optimises the files for use prior to loading into your iPhone. The optimisation process splits the large geoTIFF image file into a large number of smaller tiled JPEG image files which have been produced at a much lower resolution to reduce loading time. This optimised format is very similar to ozf2 format, which means that if you already have files of this type from a program such as OziExplorer (not version 3), they should load without the need for any optimisation.
The next step is to calibrate the file, which requires a knowledge of the grid references of the corners of the map and the grid zone name. For the Routeburn track this is 59G. The grid references of the corners of the map (extents) can be found from the LINZ website, where it is possible to download the data as a text file, spreadsheet (preferred so you can change the order of the data) or view on the screen.
World UTM Grid Zones by Alan Morton
|View an enlarged map|
MacGPS Pro first needs to convert the geoTIFF image file into PICT format, which while no smaller, is the format used internally by the program. Once imported the file is automatically calibrated by the user when the correct units (datum: NXZGD2000 and grid: NZTM2000, km, m, magnetic or true) are chosen and the file saved.
Check you have it right by finding the coordinates of a known point on the map and see whether they correspond to that on the TIFF or paper map
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This article by Bush Walker is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.