Can someone suggest a source for Canadian elevation data better or equivalent to 1 arc-second? I have a good data source for Ontario but for other provinces folks often recommend Geobase which claims that their elevation data ranges between 0.75 arc seconds to a maximum 3 arc seconds depending on latitude. However, I find that i cannot successfully generate shaded relief from the geobase data in ArcGIS. I've followed their instructions but the results are consistently un-usable. SRTM data from either cgiar.org or usgs.gov are good but I would like more detail.

alt text

Response from GeoBase: Thank you for contacting GeoBase for a follow up on improvements to avoid 'stair stepping' effects found in certain CDED data sets. Presently there is no change attributed to the status of CDED specification requirements. CDED data originates from multiple partners and data sources which make it difficult to manage a homogeneous product throughout. As you may now be aware the Z resolution in CDED files is causing the stair stepping effect. According to CDED specification standards for this scale, all elevations readings are rounded to the nearest meter of elevation for the entire Canadian coverage with approximately an elevation point every 23 metres by 16-11metres for the 1:50K scale. In flat areas, the rounding effect of the elevations causes homogeneous elevation plateaux instead of having a very gentle slope because the grid height values varies just a few centimetres. It's these adjacent plateaux that cause the stair stepping effect.
In certain cases some smoothing effect may be achieved by using the Focal Statistics tool in ArcMap Spatial Analyst toolbox, neighbourhood tools before processing CDED files. Depending on this software application you may be able to adjust viewing features with the tool menu for '' Neighbourhood=Circle, Radius=5, Units=Cell and Statistics Type=MEAN''. But I don't think there is a perfect setting for all CDED files. There is a part of trial and error in the settings for each tile. Because of this situation and the software you are using you may need to request assistance for your software provider to smooth out the look of you files. Because no perfect solution was arised from our tests, GeoBase did not provide a universal user guide for smoothing out CDED elevation data, in the Frequently Asked Question segment.

  • what is the 1 arc second equivalent in meters? I always get that messed up. Also, can you be more specific about what is unusable about the results you are getting? – matt wilkie Sep 8 '10 at 16:18
  • i beleive 1arc-second is roughly 30m resolution whereas 3 arc-second 90m. – Jakub Sisak GeoGraphics Sep 8 '10 at 20:23
  • Unfortunately, for some of the data GeoBase is the only source. For instance, the BC TRIM DEM is only available for ridiculous and unsupportable fees ($500 per 1:250k sheet, I'd guess more than $50k for whole province) otherwise. – JasonBirch Sep 14 '10 at 17:20

When generating shaded reliefs it's important to transform the elevation models from geographic lat-long to a metres based projection, Albers, Lambert and Mercator work well, else you end up with horrible shadows and gross east-west stretching deformaties. Transform the reliefs back to decimal degrees afterwards if necessary. Also instead of accepting the default 45° sun angle put it higher in the sky, about 70°, and an upper left aspect, about 315°.

I assembled the Geobase elevation models into larger tiles which are somewhat easier to use, see http://www.maphew.com/Projects/Canada_50k_Digital_Elevation_Model. The storage resolution (pixel dimensions) is 16 metre cells, not to be confused with nominal resolution which ranges from 10m to 30m+ depending on original data source and latitude.

update: here is a sample generated from 105G08 freshly downloaded from Geobase and using the above parameters in Spatial Analyst's Hillshade. Screen clip captured from Arcmap at "zoom to raster resolution" scale. smooth shaded relief

  • Thanks Matt. I never have any problems with generating shaded relief only when using GeoBase data. (Which is unfortunately the only source of wide-coverage Canadian dem i know of) I've also had conversations with their technical support staff and provided examples and documentation to them. The GeoBase 50K and 250K dem data is not usable. I`ve tried just about anything i can think of to produce usable contours and hillshade from Geobase 50K dem. Hopefuly it is something i am doing wrong so if someone has a tested procedure how to process the dem in ArcGIS please share it... – Jakub Sisak GeoGraphics Sep 8 '10 at 20:20
  • @Jakub, see updated post for what I get. What data (NTS tile) was used for the image you posted? – matt wilkie Sep 13 '10 at 18:45
  • ohhhhhh: are you using contours (lines) or elevation models (rasters) to generate your reliefs? You must use the latter, which from Geobase is CDED -- Canadian Digital Elevation Data -- and not the former. – matt wilkie Sep 13 '10 at 18:51
  • Any tile in Manitoba, try 062J05 – Jakub Sisak GeoGraphics Sep 14 '10 at 3:15
  • I heard back from Geobase and they are aware of the "staircase" anomaly. It has to do with CDED requirement to round elevation data to the nearest meter. I will post their response tomorrow. – Jakub Sisak GeoGraphics Sep 14 '10 at 3:17

Data of this resolution does not exist. It is only available on Province by Province bases; Ontario = Yes, BC = Yes, Alberta = No, Manitoba = No, Yukon = No. Have not tried other provinces.


OpenStreetMap (osm) uses CanVec Data and a combination of GeoBaseNHN

It does contain Elevation and Contours


This is the best help guide in Google Docs https://spreadsheets.google.com/ccc?key=0Am70fsptsPF2clAwc29KaXlGaGFwS1piUkxZWjc0ekE&hl=en#gid=0

It might be easier to download the OSM data and use that than re-process the Canvec

Though http://ftp2.cits.rncan.gc.ca/pub/canvec/ is the source data

| improve this answer | |

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.