Flow Direction Cell Count

Question

First post!  I am new to GIS, so bear with me.

I created a flow direction layer, and the layer has more cells than the input surface layer.  How can this be?  The reason this is a problem for me is that I am using the direction layer to calculate flow accumulation, and I would like to translate this to drainage area.

Thanks in advance

TomGebhard · Answer

Before you calculate flow direction make sure that the environment is set up not to resample anything:

These should be default or same as your surface raster
- outputCoordinateSystem 
- cellSize

Also, it's best practice to set the snapRaster to the surface raster.

That worked.  Thanks!

curtvprice · Answer

First post!  I am new to GIS, so bear with me.

I created a flow direction layer, and the layer has more cells than the input surface layer.  How can this be?  The reason this is a problem for me is that I am using the direction layer to calculate flow accumulation, and I would like to translate this to drainage area.

Thanks in advance

Before you calculate flow direction make sure that the environment is set up not to resample anything:

These should be default or same as your surface raster
- outputCoordinateSystem 
- cellSize

Also, it's best practice to set the snapRaster to the surface raster.