GIS High Grounds and Watersheds
We are learning here the following: under guidance of Michael Barton:
> Dear Mike
> If you take a look at the top two images on the Peninsular Europe site
> They cut Europe into two complementary parts: the mountain ranges and the river basins. We are starting an ecological project that uses these two visual cuts. There is a some kind of optimum elevation (for some regions, possibly on an altitude trend surface, in others, absolute elevation) that creates this contrast.
> Would it be an easy thing for you to do to make such a double mapping for the larger eco-region of
- China (East Asia)
- Mexico and Central America? Doug 08:00, 21 August 2007 (PDT)
This is incredibly simple to do in GRASS. I don't know R code, but in GRASS you can do it using r.reclass (make virtual reclass maps that act like real maps but take up next to no space), r.recode (make new maps), or r.mapcalc (map calculator to implement map algebra boolean expressions). This is a basic function of raster GIS.
If I had the map, it would take all of about 10 seconds. Come to think of it, I do have an SRTM with a 1km resolution that I could do this with if you told me the elevation cut-off values. There are other ways to do this, of course. You could pick zones of high slope (using r.slope.aspect, followed by r.reclass, r.recode, or r.mapcalc), or even differentiate between different landforms (peaks, channels, ridges, etc.) using r.param.scale.
On 8/21/07 8:06 AM, "Doug White" <firstname.lastname@example.org> wrote:
Great, I thought it would be simple. I am incredibly newbie in this: where would I find an appropriate e-map that has encoded elevations, e.g. for * Europe (to replicate the Peninsular_Europe results * China (East Asia) * Mexico and Central America? Doug 08:00, 21 August 2007 (PDT) My test-bed for developing instructions is at http://intersci.ss.uci.edu/wiki/index.php/GIS_High_Grounds_and_Watersheds Click the red link any paste a bio or cv for yourself on the wiki and also create your login. Eventually we can continue this development of a tutorial (ending in a successful outcome) onsite at the wiki
For all of Europe, I suggest 30' SRTM (shuttle radar topography mission) data. This gives a resolution of ~1km
You can get this from several places. A very easy-to-use source is the Global Landcover Facility (GLCF) at <http://glcf.umiacs.umd.edu>. They are provided as geotiff files.
You can also get them from the JPL at NASA <ftp://e0srp01u.ecs.nasa.gov/srtm/>. These are in a different format but might be of a little better quality (better filled holes,etc.) if you use version 2 or 3. IMHO, the quality issues are more important for the higher resolution SRTMs (90m and 30m resolution).
You can get 30m resolution SRTMs for the US and 90m SRTMs for the rest of the world. These are also available from the GLCF in easy to download format. At the GLCF, you can get them in latlon or in UTM projection. However, these are only the version 1 DEMs.
For the higher resolution stuff, I recommend to get the newer DEMs (version 2 or recently released version 3). These have holes filled and some other improvements. These can be had from the JPL ftp site or from a great European site CGIAR <http://srtm.csi.cgiar.org/>. From both JPL and CGIAR, the DEMs are only in latlon. So if you need them in UTM or other projection, you'll have to reproject them.
Hope this is helpful