ArcGIS for Desktop

  • Documentation
  • Pricing
  • Support

  • My Profile
  • Help
  • Sign Out
ArcGIS for Desktop

ArcGIS Online

The mapping platform for your organization

ArcGIS for Desktop

A complete professional GIS

ArcGIS for Server

GIS in your enterprise

ArcGIS for Developers

Tools to build location-aware apps

ArcGIS Solutions

Free template maps and apps for your industry

ArcGIS Marketplace

Get apps and data for your organization

  • Documentation
  • Pricing
  • Support
Esri
  • Sign In
user
  • My Profile
  • Sign Out

Help

  • Home
  • Get Started
  • Map
  • Analyze
  • Manage Data
  • Tools
  • More...

Path Distance Allocation

Available with Spatial Analyst license.

  • Summary
  • Usage
  • Syntax
  • Code Sample
  • Environments
  • Licensing Information

Summary

Calculates the nearest source for each cell based on the least accumulative cost over a cost surface, while accounting for surface distance and horizontal and vertical cost factors.

Learn more about how the path distance tools work

Usage

  • The Path Distance tools are comparable to the Cost Distance tools in that both determine the minimum accumulative travel cost from a source to each location on a raster surface. However, the Path Distance tools add more complexity to the analysis by being able to accommodate for the actual surface distance as well as other horizontal and vertical factors.

  • The input source data can be a feature class or raster.

  • When the input source data is a raster, the set of source cells consists of all cells in the source raster that have valid values. Cells that have NoData values are not included in the source set. The value 0 is considered a legitimate source. A source raster can be easily created using the extraction tools.

  • When the input source data is a feature class, the source locations are converted internally to a raster before performing the analysis. The resolution of the raster can be controlled with the Cell Size environment. By default, the resolution will be determined by the maximum cell size between the cost, surface, horizontal factor, and vertical factor input rasters. If none of these optional inputs are specified, a specific value must be set for the cell size environment.

  • When using polygon feature data for the input source data, care must be taken with how the output cell size is handled when it is coarse, relative to the detail present in the input. The internal rasterization process employs the same default Cell assignment type method as the Polygon to Raster tool, which is CELL_CENTER. This means that data not located at the center of the cell will not be included in the intermediate rasterized source output, and so will not be represented in the distance calculations. For example, if your sources are a series of small polygons, such as building footprints, that are small relative to the output cell size, it is possible that only a few of them will fall under the centers of the output raster cells, seemingly causing most of the others to be lost in the analysis.

    To avoid this situation, as an intermediate step, you could rasterize the input features directly with the Polygon to Raster tool and set a Priority field, and use the resulting output as input to the Distance tool. Alternatively, you could select a small enough cell size to capture the appropriate amount of detail from the input features.

  • To calculate allocation, source locations can have an associated value, which can be specified by the Source field parameter. If the input source is an integer raster, the default field is VALUE. If it is a feature, it will be the first integer field in the attribute table. If the input source data is a floating point raster an integer value raster parameter must be specified.

  • Cells with NoData act as barriers in the Path Distance tools. The cost distance for cells behind NoData values is calculated by the accumulative cost necessary to move around the NoData barrier. Any cell location that is assigned NoData on any one of the input rasters will receive NoData on all output rasters.

  • If the input source data and the cost raster are different extents, the default output extent is the intersection of the two. To get a cost distance surface for the entire extent, choose the Union of Inputs option on the output Extent environment settings.

  • If a Mask has been set in the environment, all masked cells will be treated as NoData values.

    When a mask has been defined in the Raster Analysis window and the cells to be masked will mask a source, the calculations will occur on the remaining source cells. The source cells that are masked will not be considered in the computations. These cell locations will be assigned NoData on all outputs (distance, allocation, and back link) rasters.

  • The output of the Aspect tool can be used as input for the Input horizontal raster.

  • The Maximum distance is specified in the same cost units as those on the cost raster.

  • For the output distance raster, the least-cost distance (or minimum accumulative cost distance) of a cell to a set of source locations is the lower bound of the least-cost distances from the cell to all source locations.

  • The default values for the Horizontal factor modifiers are:

    Keywords         Zero factor   Cut angle     Slope   Side value
    --------------   -----------   -----------   -----   ---------
    Binary           1.0            45           ~       ~
    Forward          0.5            45 (fixed)   ~       1.0
    Linear           0.5           181            1/90   ~
    Inverse linear   2.0           180           -1/90   ~
  • The default values for the Vertical factor modifiers are:

    Keyword                   Zero factor  Low cut  Height cut  Slope  Power  Cos    Sec
                                           angle    angle                     power  power            
    ------------------------  -----------  -------  ----------  -----  -----  -----  -----
    Binary                    1.0          -30      30          ~      ~      ~      ~
    Linear                    1.0          -90      90           1/90  ~      ~      ~
    Symmetric linear          1.0          -90      90           1/90  ~      ~      ~
    Inverse linear            1.0          -45      45          -1/45  ~      ~      ~
    Symmetric inverse linear  1.0          -45      45          -1/45  ~      ~      ~
    Cos                       ~            -90      90          ~      1.0    ~      ~
    Sec                       ~            -90      90          ~      1.0    ~      ~
    Cos_sec                   ~            -90      90          ~      ~      1.0    1.0
    Sec_cos                   ~            -90      90          ~      ~      1.0    1.0
  • See Analysis environments and Spatial Analyst for additional details on the geoprocessing environments that apply to this tool.

Syntax

PathAllocation (in_source_data, {source_field}, {in_cost_raster}, {in_surface_raster}, {in_horizontal_raster}, {horizontal_factor}, {in_vertical_raster}, {vertical_factor}, {maximum_distance}, {in_value_raster}, {out_distance_raster}, {out_backlink_raster})
ParameterExplanationData Type
in_source_data

The input source locations.

This is a raster or feature dataset that identifies the cells or locations to which the least accumulated cost distance for every output cell location is calculated.

For rasters, the input type can be integer or floating point.

If the input source raster is floating point, the {in_value_raster} must be set, and it must be of integer type. The value raster will take precedence over any setting of the {source_field}.

Raster Layer | Feature Layer
source_field
(Optional)

The field used to assign values to the source locations. It must be integer type.

If the {in_value_raster} has been set, the values in that input will have precedence over any setting for the {source_field}.

Field
in_cost_raster
(Optional)

A raster defining the impedance or cost to move planimetrically through each cell.

The value at each cell location represents the cost per unit distance for moving through the cell. Each cell location value is multiplied by the cell resolution while also compensating for diagonal movement to obtain the total cost of passing through the cell.

The values of the cost raster can be integer or floating point, but they cannot be negative or zero (you cannot have a negative or zero cost).

Raster Layer
in_surface_raster
(Optional)

A raster defining the elevation values at each cell location.

The values are used to calculate the actual surface distance covered when passing between cells.

Raster Layer
in_horizontal_raster
(Optional)

A raster defining the horizontal direction at each cell.

The values on the raster must be integers ranging from 0 to 360 with 0 degrees being north, or toward the top of the screen, and increasing clockwise. Flat areas should be given a value of -1. The values at each location will be used in conjunction with the {horizontal_factor} to determine the horizontal cost incurred when moving from a cell to its neighbors.

Raster Layer
horizontal_factor
(Optional)

The Horizontal Factor object defines the relationship between the horizontal cost factor and the horizontal relative moving angle.

There are several factors with modifiers from which to select that identify a defined horizontal factor graph. Additionally, a table can be used to create a custom graph. The graphs are used to identify the horizontal factor used in calculating the total cost of moving into a neighboring cell.

In the explanations below, two acronyms are used: 'HF' stands for horizontal factor, which defines the horizontal difficulty encountered when moving from one cell to the next; and 'HRMA' stands for horizontal relative moving angle, which identifies the angle between the horizontal direction from a cell and the moving direction.

The object comes in the following forms:

  • HfBinary, HfForward, HfLinear, HfInverseLinear, and HfTable.

The definitions and parameters of these are:

  • HfBinary({zeroFactor},{cutAngle})

    Indicates that if the HRMA is less than the cut angle, the HF is set to the value associated with the zero factor; otherwise, it is infinity.

  • HfForward({zeroFactor},{sideValue})

    Establishes that only forward movement is allowed. The HRMA must be greater or equal to 0 and less than 90 (0 <= HRMA < 90). If the HRMA is greater than 0 and less than 45 degrees, the HF for the cell is set to the value associated with the zero factor. If the HRMA is greater than or equal to 45 degrees, then the side value modifier value is used. The HF for any HRMA equal to or greater than 90 degrees is set to infinity.

  • HfLinear({zeroFactor},{cutAngle},{slope})

    Specifies that the HF is a linear function of the HRMA.

  • HfInverseLinear({zeroFactor},{cutAngle},{slope})

    Specifies that the HF is an inverse linear function of the HRMA.

  • HfTable(inTable)

    Identifies that a table file will be used to define the horizontal factor graph used to determine the HFs.

The Modifiers to the horizontal keywords are:

  • {zeroFactor}—Establishes the horizontal factor used when the HRMA is 0. This factor positions the y intercept for any of the horizontal factor functions.
  • {cutAngle}—Defines the HRMA angle beyond which the HF will be set to infinity.
  • {slope}—Establishes the slope of the straight line used with the HfLinear and HfInverseLinear horizontal-factor keywords. The slope is specified as a fraction of rise over run (for example, 45 percent slope is 1/45, which is input as 0.02222).
  • {sideValue}—Establishes the HF when the HRMA is greater than or equal to 45 degrees and less than 90 degrees when the HfForward horizontal-factor keyword is specified.
  • inTable—Identifies the name of the table defining the HF.

Horizontal factor
in_vertical_raster
(Optional)

A raster defining the z-values for each cell location.

The values are used for calculating the slope used to identify the vertical factor incurred when moving from one cell to another.

Raster Layer
vertical_factor
(Optional)

The Vertical factor object defines the relationship between the vertical cost factor and the vertical relative moving angle (VRMA).

There are several factors with modifiers from which to select that identify a defined vertical factor graph. Additionally, a table can be used to create a custom graph. The graphs are used to identify the vertical factor used in calculating the total cost for moving into a neighboring cell.

In the explanations below, two acronyms are used: 'VF' stands for vertical factor, which defines the vertical difficulty encountered in moving from one cell to the next; and 'VRMA' stands for vertical relative moving angle, which identifies the slope angle between the FROM or processing cell and the TO cell.

The object comes in the following forms:

  • VfBinary, VfLinear, VfInverseLinear, VfSymLinear, VfSymInverseLinear, VfCos, VfSec, VfSec, VfCosSec, VfSecCos, VfTable.

The definitions and parameters of these are:

  • VfBinary({zeroFactor},{lowCutAngle},{highCutAngle})

    Specifies that if the VRMA is greater than the low-cut angle and less than the high-cut angle, the VF is set to the value associated with the zero factor; otherwise, it is infinity.

  • VfLinear({zeroFactor},{lowCutAngle},{highCutAngle},{slope})

    Indicates that the VF is a linear function of the VRMA.

  • VfInverseLinear({zeroFactor},{lowCutAngle},{highCutAngle},{slope})

    Indicates that the VF is an inverse linear function of the VRMA.

  • VfSymLinear({zeroFactor},{lowCutAngle},{highCutAngle},{slope})

    Specifies that the VF is a linear function of the VRMA in either the negative or positive side of the VRMA, respectively, and the two linear functions are symmetrical with respect to the VF (y) axis.

  • VfSymInverseLinear({zeroFactor},{lowCutAngle},{highCutAngle},{slope})

    Specifies that the VF is an inverse linear function of the VRMA in either the negative or positive side of the VRMA, respectively, and the two linear functions are symmetrical with respect to the VF (y) axis.

  • VfCos({lowCutAngle},{highCutAngle},{cosPower})

    Identifies the VF as the cosine-based function of the VRMA.

  • VfSec({lowCutAngle},{highCutAngle},{secPower})

    Identifies the VF as the secant-based function of the VRMA.

  • VfCosSec({lowCutAngle},{highCutAngle},{cosPower},{secPower})

    Indicates that the VF is the cosine-based function of the VRMA when the VRMA is negative and the secant-based function of the VRMA when the VRMA is nonnegative.

  • VfSecCos({lowCutAngle},{highCutAngle},{secPower},{cos_power})

    Specifies that the VF is the secant-based function of the VRMA when the VRMA is negative and the cosine-based function of the VRMA when the VRMA is nonnegative.

  • VfTable(inTable)

    Identifies that a table file will be used to define the vertical-factor graph used to determine the VFs.

The Modifiers to the vertical parameters are:

  • {zeroFactor}—Establishes the vertical factor used when the VRMA is zero. This factor positions the y-intercept of the specified function. By definition, the zero factor is not applicable to any of the trigonometric vertical functions (Cos, Sec, Cos_Sec, or Sec_Cos). The y-intercept is defined by these functions.
  • {lowCutAngle}—Defines the VRMA angle below which the VF will be set to infinity.
  • {highCutAngle}—Defines the VRMA angle above which the VF will be set to infinity.
  • {slope}—Establishes the slope of the straight line used with the VfLinear and VfInverseLinear parameters. The slope is specified as a fraction of rise over run (for example, 45 percent slope is 1/45, which is input as 0.02222).
  • inTable—Identifies the name of the table defining the VF.
Vertical factor
maximum_distance
(Optional)

Defines the threshold that the accumulative cost values cannot exceed.

If an accumulative cost distance value exceeds this value, the output value for the cell location will be NoData. The maximum distance defines the extent for which the accumulative cost distances are calculated.

The default distance is to the edge of the output raster.

Double
in_value_raster
(Optional)

The input integer raster that identifies the zone values that should be used for each input source location.

For each source location (cell or feature), the value defined by the {in_value_raster} will be assigned to all cells allocated to the source location for the computation. The value raster will take precedence over any setting for the {source_field}.

Raster Layer
out_distance_raster
(Optional)

The output path distance raster.

The output path distance raster identifies, for each cell, the least accumulative cost distance, over a cost surface to the identified source locations, while accounting for surface distance as well as horizontal and vertical surface factors.

A source can be a cell, a set of cells, or one or more feature locations.

The output raster is of floating point type.

Raster Dataset
out_backlink_raster
(Optional)

The output cost back-link raster.

The back-link raster contains values of 0 through 8, which define the direction or identify the next neighboring cell (the succeeding cell) along the least accumulative cost path from a cell to reach its least cost source, while accounting for surface distance as well as horizontal and vertical surface factors.

If the path is to pass into the right neighbor, the cell will be assigned the value 1, 2 for the lower right diagonal cell, and continuing clockwise. The value 0 is reserved for source cells.

Back-link positions
Raster Dataset

Return Value

NameExplanationData Type
out_allocation_raster

The output path distance allocation raster.

This raster identifies the zone of each source location (cell or feature) that could be reached with the least accumulative cost, while accounting for surface distance and horizontal and vertical cost factors.

The output raster is of integer type.

Raster

Code Sample

PathAllocation example 1 (Python window)

The following Python Window script demonstrates how to use the PathDistanceAllocation tool.

import arcpy
from arcpy import env
from arcpy.sa import *
env.workspace = "C:/sapyexamples/data"
pathAlloc = PathAllocation("observers.shp", "costraster", "elevation", "backlink2",
                            HfForward(0.5, 1.0), "focalcost.tif", VfBinary(1.0, -30, 30),  
                            25000, "eucdirout", "FID", "c:/sapyexamples/output/optpathdist", 
                            "c:/sapyexamples/output/optpathbl")
pathAlloc.save("c:/sapyexamples/output/allocpath")
PathAllocation script example

Calculates the nearest source for each cell based on the least accumulative cost over a cost surface, while accounting for surface distance and horizontal and vertical cost factors.

# Name: PathAllocation_Ex_02.py
# Description: Calculates, for each cell, its nearest source based 
#              on the least accumulative cost over a cost surface, 
#              while accounting for surface distance and horizontal 
#              and vertical cost factors. 
# 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
inSource = "observers.shp"
costRast = "costraster"
surfaceRast = "elevation"

# The horizontal factor
inHoriz = "backlink2"
# Create the HfForward Object
zeroFactor = 0.5
sideValue = 1.0
myHorizFactor = HfForward(zeroFactor, sideValue)

#The vertical factor
inVertical = "focalcost.tif"
# Create the VfBinary Object
zeroFactor = 1.0
lowCutAngle = -30
highCutAngle = 30
myVerticalFactor = VfBinary(zeroFactor, lowCutAngle, highCutAngle)

maxDist = 25000
valRaster = "eucdirout"
sourceField = "FID"
optPathDistOut = "c:/sapyexamples/output/optdistpath"
optPathBLOut = "c:/sapyexamples/output/pathblinkout"

# Check out the ArcGIS Spatial Analyst extension license
arcpy.CheckOutExtension("Spatial")

# Execute PathAllocation
pathAlloc = PathAllocation(inSource, costRast, surfaceRast, 
                           inHoriz, myHorizFactor, inVertical, myVerticalFactor, 
                           maxDist, valRaster, sourceField, 
                           optPathDistOut, optPathBLOut)

# Save the output 
pathAlloc.save("c:/sapyexamples/output/allocpath02")

Environments

  • Auto Commit
  • Cell Size
  • Compression
  • Current Workspace
  • Extent
  • Geographic Transformations
  • Mask
  • Output CONFIG Keyword
  • Output Coordinate System
  • Raster Statistics
  • Scratch Workspace
  • Snap Raster
  • Tile Size

Licensing Information

  • ArcGIS for Desktop Basic: Requires Spatial Analyst
  • ArcGIS for Desktop Standard: Requires Spatial Analyst
  • ArcGIS for Desktop Advanced: Requires Spatial Analyst

Related Topics

  • An overview of the Distance toolset
  • Path Distance
  • Path Distance Back Link
Feedback on this topic?

ArcGIS for Desktop

  • Home
  • Documentation
  • Pricing
  • Support

ArcGIS Platform

  • ArcGIS Online
  • ArcGIS for Desktop
  • ArcGIS for Server
  • ArcGIS for Developers
  • ArcGIS Solutions
  • ArcGIS Marketplace

About Esri

  • About Us
  • Careers
  • Insiders Blog
  • User Conference
  • Developer Summit
Esri
© Copyright 2016 Environmental Systems Research Institute, Inc. | Privacy | Legal