Geographic Information Systems Stack Exchange is a question and answer site for cartographers, geographers and GIS professionals. It only takes a minute to sign up.
Sign up to join this community
I have two pour points in a stream network created using the flow accumulation methodology in ArcMap.
When I use the watershed tool with this pour point shapefile, I get a watershed between these two points. What exactly is this watershed?
I've tried searching on the ESRI site, but I can't seem to pinpoint the exact answer.
Edit: I don't want two catchments here. I want an area of everything that flows from the "upper pour point" to the "lower point." Picture included.
Watershed doesn't really work that well with only two points. As its name implies, it is supposed to delineate watersheds. To answer your question, the watershed you created is a subbasin. That is, it is the contributing area above the bottom spill point and below the top spill point. The tool is designed to have enough spill points as input so that it can merge together subbasins into watersheds based on a tolerance that you give it.
That all said, if all you want to see is that small area, maybe that is all you need. Assuming the initial raster that you created the spill points from covered a big enough area to provide accurate enough spill points for your purposes, and you included the value field (since you are using features for spill points), what you did should have given you what you wanted, i.e. a map of what cells flow to the bottom spill point from the top spill point.
Just keep in mind that if you didn't include a very large area while determining your spill points, that the small area you used may not be correct. Things could happen in nearby areas off your raster that would affect the accumulation pattern.
The help file has a good picture. http://pro.arcgis.com/en/pro-app/tool-reference/spatial-analyst/how-watershed-works.htm
