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About the Department
Maps & GIS Data
This page talks about the Digital Elevation Models (DEMs), which you can download from the Geomatics Yukon ftp site.
- Derivative Products
- Why Free?
- Software Tools for DEMs
The Department of the Environment GIS (ENVY GIS) 30 Meter DEM is a Digital Elevation Model spanning the entire Yukon and a bit beyond in some places. It was interpolated from the digital 1:50,000 Canadian National Topographic Database (NTDB Edition 2) contour and watercourse layers using 30 meter cells (aka pixels). For refinement and added quality we also incorporated ancillary data not part of the NTDB (more details below).
There is also a 90m DEM is resampled from the 30m and designed for use wherever you have need of a 1:250k scale DEM, provided you keep the following caution in mind:
Caveat: In many cases DEMs are used in conjunction with base topographic data (contours, lakes, rivers, roads, etc.), that is, topographic data are often superimposed or overlaid on top of DEMs and their derivatives. The spatial extent (1° latitude by 2° longitude) and cell size of the 90m DEM make them roughly equivalent to 1:250,000 scale NTS maps. However, because the data used to derive the 90m DEMs (1:50,000 NTS) differ from the 1:250,000 scale NTS data, topographic features in the 1:250,000 scale NTS do not line up when overlaid on top of 90m DEMs.
In our view the Environment Yukon DEMs are better quality but no definitive study has been undertaken to prove or disprove this. You are welcome to form your own opinion; in doing so you might find the RRGIS vs CDED and What's The Difference pages helpful. (historical links courtesy of the Wayback Internet Archive).
In order to improve the quality of the DEMs we incorporated some ancillary datasets, namely:
- Lakes with known elevations were converted to contour lines and used in the interpolation process. After the DEM was created the interior of the lake polygons were replaced with the lake elevation values.
- BC TRIM data.
- Alaska 7.5 minute DEMs.
Other complementary sources which we looked at but decided not to incorporate into this version of the DEM due to undesirable artifacting are the Aerial Survey Database and Geodetic Control Points [sorry, missing the link]. CDED incorporates these complementary sources.
When first released the hires 30m version was available only to licensed NTDB holders. That restriction was lifted in 2005 and now all versions of the elevation model are free and libre.
The DEMs are free, in both the sense of cost and of liberty. You are free to use these DEMs in any way you see fit including commercial endeavours. It would be courteous to inform us what you are doing with them and to credit the Yukon Department of Environment, Information Management & Technology Branch where applicable.
The only derivative product currently available are the Shaded Relief images.
Also known as Sunshade or Hillshade images, shaded relief images are the most popular form of visually representing a DEM. Indeed many view a shaded relief image and mistakenly think they are seeing the DEM itself. A shaded relief image does not contain elevation values, rather each pixel's brightness value is an expression of it's reflectance (slope and aspect) relative to the light source (azimuth and zenith).
Sample Relief Image
Sample DEM Image
Technically speaking, this DEM image does not contain any elevation values either. Rather the brightness of an individual pixel indicates it's vertical "position" relative to the minimum and maximum values present in the image which are black and white respectively (in this case 500m and 2200m). A pixel's "height" can be then calculated from it's relative value.
Anyway the point is, if you want to do silicon computer analytical work you need the DEM. If you want to use the biological analytical device attached to your optic nerve, use the relief image.
The relief images are in GeoTIFF format utilizing TIFF Compression 2. The images should be easily opened by any graphics editing/viewing program and most GIS/RS programs.
A seamless mosaick of the 90m shaded relief with 90m, 300m and 500m can be downloaded from the Geomatics Yukon ftp site ftp://ftp.geomaticsyukon.ca/. For those who think smaller is bigger, there are also 30m Relief Images (~12mb each)
For licensed 50k NTDB users you may want to view the problems we encountered with the source data. Download the Errata metadata package (applies to NTDB Edition 2.1) which lists all the gross data blunders we encountered in the base data and what actions we took to correct them, if any. Users are encouraged to add to this meta-cover and send it back to the DEM guy if you find any new errors.
For more information, consult the the Errata ReadMe.
Availability of free, high quality, digital geospatial data will stimulate and encourage the local knowledge based economy. If you are a local Yukon resident, business or organization and have developed DEM derived products or services, please let us know so we can add a link to your site here and show some examples which are more relevant than the haphazard list above.
We used to keep a list of software tools for working with DEMs, but now we just send people off to John Child's TerrainMap.com, who is doing a far better job than we ever did.