Available with Spatial Analyst license.
Overview
Defines the neighbor that is the next cell on the least accumulative cost path to the leastcost source, while accounting for surface distance along with horizontal and vertical cost factors.
Notes
The Path Distance functions are comparable to the Cost Distance functions in that both determine the minimum accumulative travel cost from or to a source for each location on a raster surface. However, the Path Distance functions add more complexity to the analysis by accommodating the actual surface distance as well as other horizontal and vertical factors.
Cells with NoData act as barriers in the Path Distance fuctions. 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.
The Maximum Distance is specified in the same cost unit as the Cost Raster.
For the output raster, the leastcost distance (or minimum accumulative cost distance) of a cell to a set of source locations is the lower bound of the leastcost distances from the cell to all source locations.
The default values for the Horizontal factor modifiers are the following:
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 the following:
Keyword Zero Low High Slope Power Cos Sec factor cut cut power power angle angle         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
The output of the Aspect function can be used as input for Input horizontal raster.
The characteristics of the source, or the movers from or to a source, can be controlled by specific parameters. The Source cost multiplier parameter determines the mode of travel or magnitude at the source, Source start cost sets the starting cost before the movement begins, Source resistance rate is a dynamic adjustment accounting for the impact of accumulated cost, for example, simulating how much a hiker is getting fatigued, and Source capacity sets how much cost a source can assimilate before reaching its limit. The Travel direction identifies if the mover is starting at a source and moving to nonsource locations, or is starting at nonsource locations and moving back to a source.
If any of the source characteristics parameters are specified using a field, the source characteristic will be applied on a sourcebysource basis, according to the information in the given field for the source data. When a keyword or a constant value is given, it will be applied to all sources.
If Source start cost is specified and the Travel direction is Travel from source, the source locations on the output cost distance surface will be set to the value of Source start cost; otherwise, the source locations on the output cost distance surface will be set to zero.
This function supports parallel processing. If your computer has multiple processors or processors with multiple cores, better performance may be achieved, particularly on larger datasets. See Parallel processing with Spatial Analyst for more details on this capability and how to configure it.
When using parallel processing, temporary data will be written to manage the data chunks being processed. The default temp folder location will be on your local C drive. You can control the location of this folder by setting up a system environment variable named TempFolders and specifying the path to a folder to use (for example, E:\RasterCache). If you have admin privileges on your machine, you can also use a registry key (for example, [HKEY_CURRENT_USER\SOFTWARE\ESRI\ArcGISPro\Raster]).
By default, this function will use 50 percent of the available cores. If the input data is smaller than 5,000 by 5,000 cells, fewer cores may be used. You can control the number of cores the tool uses with the Parallel processing factor environment.
Parameters
Parameter name  Description 

Source Raster (Required)  The input source locations. This is a raster dataset that identifies the cells or locations from which the least accumulated cost distance for every output cell location is calculated. It can be an integer or a floatingpoint type. 
Cost Raster (Required)  A raster defining the cost or impedance to move planimetrically through each cell. The value at each cell location represents the costperunit distance for moving through it. Each cell location value is multiplied by the cell resolution, and also compensates 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. 
Surface Raster  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. 
Horizontal Raster  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. 
Horizontal Factor  Defines the relationship between the horizontal cost factor and the horizontal relative moving angle (HRMA). There are several factors with modifiers you can 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: HF and HRMA. HF stands for horizontal factor, which defines the horizontal difficulty encountered when moving from one cell to the next. HRMA stands for horizontal relative moving angle, which identifies the angle between the horizontal direction from a cell and the moving direction. Horizontal factor types include the following:
Modifiers to the horizontal factors include the following:

Vertical Raster  Defines the relationship between the vertical cost factor and the vertical relative moving angle (VRMA). The values are used for calculating the slope used to identify the vertical factor incurred when moving from one cell to another. 
Vertical Factor  Defines the relationship between the vertical cost factor and the vertical relative moving angle (VRMA). There are several factors with modifiers you can 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 and VRMA. VF stands for vertical factor, which defines the vertical difficulty encountered in moving from one cell to the next. VRMA stands for vertical relative moving angle, which identifies the slope angle between the FROM, or processing, cell and the TO cell. Vertical factor types include the following:
Modifiers to the vertical keywords include the following:

Maximum Distance  The threshold that the accumulative cost values cannot exceed. If an accumulative cost distance 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 extent of the output raster. 
Multiplier to Apply to Costs  A multiplier to apply to the cost values. This parameter allows for control of the mode of travel or the magnitude at a source. The greater the multiplier, the greater the cost to move through each cell. The values must be greater than zero. The default is 1. A numeric (double) value or a field from the Source Raster can be used for this parameter. 
Start Cost  The starting cost from which to begin the cost calculations. This parameter allows for the specification of the fixed cost associated with a source. Instead of starting at a cost of 0, the cost algorithm will begin with the value specified. The value must be zero or greater. The default is 0. 
Accumulative Cost Resistance Rate  This parameter simulates the increase in the effort to overcome costs as the accumulative cost increases. It is used to model fatigue of the traveler. The growing accumulative cost to reach a cell is multiplied by the resistance rate and added to the cost to move into the subsequent cell. It's a modified version of a compound interest rate formula that's used to calculate the apparent cost of moving through a cell. As the value of the resistance rate increases, it increases the cost of the cells that are visited later. The greater the resistance rate, the higher the cost to reach the next cell, which is compounded for each subsequent movement. Since the resistance rate is similar to a compound rate and generally the accumulative cost values are very large, small resistance rates are suggested, such as 0.005 or even smaller, depending on the accumulative cost values. The value must be greater than zero. The default capacity is to the edge of the output raster. 
Capacity  Defines the cost capacity for the traveler for a source. The cost calculations continue for each source until the specified capacity is reached. The value must be greater than zero. The default capacity is to the edge of the output raster. 
Travel Direction  Defines the direction of the traveler when applying the source resistance rate and the source starting cost.
Either specify the From Source or To Source keyword, which will be applied to all sources, or specify a field in the Source Raster that contains the keywords to identify the direction of travel for each source. That field must contain the string FROM_SOURCE or TO_SOURCE. 
Environment settings
Geoprocessing environment settings for global functions are controlled at the application level. Setting processing environments in ArcGIS Pro can be done by clicking the Environments button on the Analysis tab. See Analysis environments and Spatial Analyst for additional details on environment settings.
The following environments are supported by this global function: