Available with Spatial Analyst license.
Summary
Calculates the upstream or downstream distance, or weighted distance, along the flow path for each cell.
Usage
A primary use of the Flow Length tool is to calculate the length of the longest flow path within a given basin. This measure is often used to calculate the time of concentration of a basin. This would be done using the UPSTREAM option.
The tool can also be used to create distance-area diagrams of hypothetical rainfall and runoff events using the weight raster as an impedance to movement downslope.
The value type for the Flow Length output raster is floating point.
See Analysis environments and Spatial Analyst for additional details on the geoprocessing environments that apply to this tool.
Syntax
FlowLength(in_flow_direction_raster, {direction_measurement}, {in_weight_raster})
Parameter | Explanation | Data Type |
in_flow_direction_raster | The input raster that shows the direction of flow out of each cell. The flow direction raster can be created using the Flow Direction tool. | Raster Layer |
direction_measurement (Optional) | The direction of measurement along the flow path.
| String |
in_weight_raster (Optional) | An optional input raster for applying a weight to each cell. If no weight raster is specified, a default weight of 1 will be applied to each cell. For each cell in the output raster, the result will be the number of cells that flow into it. | Raster Layer |
Return Value
Name | Explanation | Data Type |
out_raster | The output raster that shows for each cell the upstream or downstream distance along a flow path. | Raster |
Code sample
FlowLength example 1 (Python window)
This example Calculates the downstream distance along the flow path for each cell.
import arcpy
from arcpy import env
from arcpy.sa import *
env.workspace = "C:/sapyexamples/data"
outFlowLength = FlowLength("flowdir", "DOWNSTREAM", "")
outFlowLength.save("c:/sapyexamples/output/outflowlen01")
FlowLength example 2 (stand-alone script)
This example Calculates the downstream distance along the flow path for each cell.
# Name: _Ex_02.py
# Description:
# Requirements: Spatial Analyst Extension
# Import system modules
import arcpy
from arcpy import env
from arcpy.sa import *
# Set environment settings
env.workspace = "C:/sapyexamples/data"
# Set local variables
inFlowDirectionRaster = "flowdir"
inWeightRaster = ""
directionType = "DOWNSTREAM"
# Check out the ArcGIS Spatial Analyst extension license
arcpy.CheckOutExtension("Spatial")
# Execute
outFlowLength = FlowLength(inFlowDirectionRaster, directionType, inWeightRaster)
# Save the output
outFlowLength.save("c:/sapyexamples/output/outflowlen02.tif")
Environments
Licensing information
- Basic: Requires Spatial Analyst
- Standard: Requires Spatial Analyst
- Advanced: Requires Spatial Analyst