I need to delineate the Chesapeake Bay watershed. For this reason, I took 16 tiles of DEM production(Arcgrid) from USGS database and merge them through Mosaic Database. I ran spatial analyst toolbox (Fill, Flow Direction, Flow Accumulation respectively) with the same spatial references as that of dem datasets (GCS_North_American_1983). Now, when I want to define pour point Shapefile to finalize watershed delineation, It can not snap the cell with the high accumulation. I am sure that Geographic Coordination System is same for my all layers. But when I want to assign relevant cells into the Shapefile of pour-points, it show a warning in which alert for inconsistency between Shapefile and one of the layers (Attachment-1). Also the result of flow accumulation doesn't seem to be satisfactory (Please see Attachment-2,3).
Is there any help you can give me. I don't know where the problem comes from.
Thank you very much