I am trying to generate flow direction from DEM. However I am getting some vales as 80 and 129, though it should be only from 1, 2, 4, 8,16, 32, 64, 128

What could be the reason for this error? How to resolve it?

Edit: Original DEM is at 90m resolution, whereas I am generating fdr at 0.25 degree spatial resolution by setting the cell size as 0.25 degree in raster analysis.

1 Answer 1


This from the flow direction tool help in ArcGIS 10.4:

If a cell has the same change in z-value in multiple directions and that cell is part of a sink, the flow direction is referred to as undefined. In such cases, the value for that cell in the output flow direction raster will be the sum of those directions. For example, if the change in z-value is the same both to the right (flow direction = 1) and down (flow direction = 4), the flow direction for that cell is 1 + 4 = 5. Cells with undefined flow direction can be flagged as sinks using the Sink tool.


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