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I am trying to replicate a flow length calculation in arcmap 10.2. I have an elevation raster with a pixel range from 0 to 3038.96m (32 bit). When I run the flow direction calculation, the pixel range drops to 0-255 (8 bit). I must be losing information that will affect my flow length calculation (I have a flow length calculation that has been completed that I'm trying to match)--how do I prevent this? I've tried searching in environment settings but I haven't found how to change my pixel range.

I'm fairly new to GIS.

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The flow direction is indeed an 8 bit image, irrespective of your input (32 or 64 bit float), from the Esri help page:

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From the centre pixel (blue) the value indicates which way the flow will go from 1 (East) to 128 (Northeast)..

From flow direction you need to proceed to Flow Accumulation or Flow Length which uses this direction raster to calculate the flow from each cell into the next; as this cell flows into another then that cell flows into the next one... from that accumulation and length can be gained.

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The very first step is Fill. It fills sinks in elevation model. Next - flow direction on filled DEM. After that you can do all other things, like flow length, using flow direction.

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