I downloaded some tiles covering North Wales, gridded and merged them in ArcGIS and hillshaded the result with 3D Analyst. All fine so far - but taking a closer look (see attachment) I've got some curious worm like features appearing.
Am I doing something wrong with the data, only as a native of these parts I don't recall seeing anything like this on the ground.
Snowdon is at bottom left.
Unfortunately GDEM (ASTER DEM) is not as good as I thought in a beginning. It is a result of automatic optical stereo processing. SRTM at least has much less noisy data. Anyway I can’t use neither SRTM, no GDEM , cause normally I need the ground surface data (DTM) without influence of forest and build-up areas. But, definitely for demonstration, prior calculations and studying it’s a good data, because it’s free!