Dear Morten Nielsen, Thank for your answer! Actually, I try to import roughness from Wed-database, but it not conincide with the background was imported. And I think roughess map is importance in my case because the elevation is not change too much. I read in manual, it has some information to made me quite hesistance when decide to digitize the roughness: - "Shouldn't digitize too large with few width meter, and the rest area digitize too small". So, in this situation with many house focus along the river and road - how to deal with this? Should I digitize detail with this site? And I should consider the site with how much area (length & width) to decide the roughness? Best regard, Vinh Le Thanh
