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Accessibility Toolbox for R and ArcGIS

Overview

This repository contains the tools, code, and data to support the paper Accessibility Toolbox for R and ArcGIS published in Transport Findings at DOI 10.32866/8416.

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The Accessibility Toolbox contains three tools:

  1. The first is the Accessibility Calculator Python toolbox for ArcGIS Pro and 10x that simplifies the steps involved in a place-based accessibility workflow. The Pro version of the tool is written for multiprocessing. As of version 2.0, the 10x tool has been moved to the legacy tools folder. Follow these steps to add the .pyt toolbox to your project or edit and run via the command line.

  2. The second is an interactive Accessibility Toolbox R Notebook that visualizes the 5 impedance functions from Kwan (1998) and 28 impedance measures to aid in the selection and customization of accessibility cost functions. Customized parameters can be implemented in the ArcGIS tool's python code.

  3. The third is the Accessibility Calculator for R that builds on the original R notebook's code to incorporate an open and reproducible workflow for calculating accessibility using the new r5r tool.

Updates

See version history for previous releases

Calculating Accessibility in ArcGIS

The Accessibility Calculator has several inputs:

Network Details

  • Input Network Dataset: the input Network Analyst network dataset for your analysis
  • Travel Mode (Pro): the travel mode for your analysis from your network dataset
  • Cutoff Value: the travel time value at which to stop searching for destinations for a given origin
  • Departure Time (optional): a time of departure from the origins; useful for analyses with traffic or GTFS transit scheduling
  • Impedance Measure: a selection of one or more impedance measures; refer to the R Notebook for guidance on selecting a measure

Origins

  • Origins: a feature class representing origin locations i; can be point or polygon
  • Origins ID Field: a unique identifier for your input origins; can be any type of field
  • Origins Network Search Tolerance: the search tolerance for locating the input features on the network; features that are outside the search tolerance are left unlocated
  • Origins Network Search Criteria: restricts the search to particular source feature classes in your network dataset; useful if you don't want to find features that may be unsuited for a network location
    • for example, if you have created a transit network using the Add GTFS to Network Dataset tool and want your origins to locate on streets while avoiding other feature classes like transit lines, you could input these expressions (using default names for the GTFS tool) into the value table: Streets_UseThisOne with a snap type of SHAPE; Stops and NONE; Stops_Snapped2Streets and NONE; Transit_Network_ND_Junctions and NONE; Connectors_Stops2Streets and NONE; and TransitLines and NONE (see example for Pro)
    • see the ArcGIS Add Locations reference for more guidance and examples on setting a search_criteria parameter
  • Origins Network Search Query (optional): specifies a query to restrict the search to a subset of the features within a network source feature class; useful if you don't want to locate on particular features
    • for example, if you do not want your input origins to locate on major highways, you could input Streets with the expression FREEWAY=0
    • in the example data, if you do not want origins to locate on tunnels or bridges, you could input the expressions NYC_OSM_Walk and tunnel<>'yes' and NYC_OSM_Walk and bridge<>'yes' into the value table (see example for Pro)
    • see the ArcGIS Add Locations reference for more guidance and examples on setting a search_query parameter

Destinations

  • Destinations: a feature class representing destination locations j; can be point or polygon
  • Destinations ID Field: a unique identifier for your input destinations; can be any type of field
  • Destination Opportunities Field: a numeric field containing the opportunities Oj available at the destination, such as the number of jobs
  • Destinations Network Search Tolerance: same notes as the Origins Network Search Tolerance
  • Destinations Network Search Criteria: same notes as the Origins Network Search Criteria
  • Destinations Network Search Query (optional): same notes as the Origins Network Search Query

General Settings

  • Output Work Folder: the folder where the output geodatabase and multiprocessing workers folder will be created; working files generated during large analyses can require many gigabytes of disk space but they are automatically deleted once the tool finishes
  • Name of Output Analysis Geodatabase: name for the output geodatabase containing the scratch working files and the final tool output
  • Origins Maximum Batch Size: maximum size of each batch of origins for multiprocessing and controlling memory/disk use; some optimization may occur if the number of observations can be spread over the available processes within your set maximum batch size ((n/(cpus-1))+1 if n/(cpus-1) <= batch size), otherwise it adheres to n/batch size
  • Delete OD lines where i = j? (optional): if selected, the tool will delete any origin-destination lines or pairs where the origin was the same as the destination; useful if you only want to calculate access to opportunities that are external to the origins
  • Join output back to origins? (optional): if selected, joins the accessibility output back to the input origins

Selecting an Impedance Function in R

Using the interactive R Notebook, users can explore 5 impedance functions:

  • inverse power
  • negative exponential
  • modified Gaussian
  • cumulative opportunities rectangular
  • cumulative opportunities linear

Each function is specified with several different impedance parameters for a total of 28 different impedance measures.

Customizing or Adding Your Impedance Measure to the Tool

Users can add or change the impedance functions in the ArcGIS Accessibility Calculator by editing the parameters.py file. This file specifies the different impedance functions and stores relevant parameters in the dictionary p. Using the examples of the POW0_8 and CUMR10 impedance measures, each dictionary entry contains the following elements:

p = {
    "POW0_8": {"f": "power", "b0": 0.8}, 
    "CUMR10": {"f": "cumr", "t_bar": 10}
    }

  • POW0_8 and CUMR10: the names of the impedance measures

  • "f": the key f indexes the value of the impedance function for the impedance measure; in the case of POW0_8, the "pow" string refers to the inverse power function; for CUMR10 the function is "cumr". Available functions are:

    • power: inverse power
    • neg_exp: negative exponential
    • mgaus: modified Gaussian
    • cumr: cumulative opportunities rectangular
    • cuml: cumulative opportunities linear

  • "b0": the key b0 indexes the value of the beta parameter for the impedance measure that will be input into the impedance function

    • in the case of the POW0_8 measure, 0.8 refers to a beta value of 0.8

  • "t_bar": the key "t_bar" indexes the value of the travel time window for the cumulative impedance functions

    • in the case of the CUMR10 measure, 10 refers to a travel time window of 10 minutes

  • if you make any additions of functions to the parameters.py file, you must update the list of impedance functions in the Accessibility_Toolbox_Pro_MP.pyt Python Toolbox. The list of function names starts on Line 223.

References

Higgins, C. D. (2019). Accessibility toolbox for R and ArcGIS. Transport Findings. https://doi.org/10.32866/8416

Kwan, M. P. (1998). Space-time and integral measures of individual accessibility: A comparative analysis using a point-based framework. Geographical Analysis, 30(3), 191-216. https://doi.org/10.1111/j.1538-4632.1998.tb00396.x

License

Creative Commons License
This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.