I am doing watershed delineation at the continental scale using a GTOPO30 DEM, projected spatial reference WGS_WGS_1984_UTM_Zone_15N. Using Arc10.... My basic workflow using ArcHydro tools: Project raster (as above)-- fill-- flow direction--flow accumulation--pick pour points--make watershed--TRY to measure watershed area 
For instance, the number of pixels in my Mississippi watershed are much greater (~4.8 million pixels, whereas published areal extent is ~2.89 million km^2). I noted cell size in DEM properties reads (x,y) = 806.6814..., 806.6814.. I was under the impression GTOPO30 had 1 km cellsize? Is there a way to use raster math/calculator to calculate upstream area or watershed area given the x,y cellsize?
What other pitfalls might I encounter with the basic workflow from above?
Thank you so much,
C
أكثر...
For instance, the number of pixels in my Mississippi watershed are much greater (~4.8 million pixels, whereas published areal extent is ~2.89 million km^2). I noted cell size in DEM properties reads (x,y) = 806.6814..., 806.6814.. I was under the impression GTOPO30 had 1 km cellsize? Is there a way to use raster math/calculator to calculate upstream area or watershed area given the x,y cellsize?
What other pitfalls might I encounter with the basic workflow from above?
Thank you so much,
C
أكثر...