Hi,

For what I can see France Digital Terrain Model resolution is good enough to be viewed at 1:100.000 scale and be close to 1 sample per pixel on the other hand Spain DTM roughly is 20 times less dense, there is an official source (Instituto Geografico Nacional / National Geographic Institute) available at 200, 25 and 5 meters per pixel for the whole Spanish territory.

Is there any chance you could use that source (it is free for personal use but I believe it is paid for commercial use) to improve the actual SD?

http://www.ign.es/ign/layoutIn/modeloDigitalTerreno.do

Thanks

Isaac