Network analysis in ArcPython

Abstract

Transportation distance is a primary indicator of the population served by a given location. For instance, most people would probably drive 5 miles to get to a park or mental health clinic, but many less would choose to drive 50 miles. While some locations, like salons or retail stores, may want to target specific populations, other locations, like WIC centers, hospitals, or parks, aim to serve all populations equally. This toolkit provides an easy means with which to identify groups of people that are better or worse served by any given facility. Using census data, road network data, and the locations of facilities, the toolkit calculates, per county, the percentage of a given demographic within a user-specified driving time or distance from a facility location. The example included in this report calculates the county-by-county access of the total population, black residents, and single mothers to WIC centers in New York. However, this toolkit can calculate the served demographics of any facility type, with any amount of distance, and with respect to any census data (race, income, household type, education, or age). For instance, one could determine whether a youth fashion brand is properly targeting youth, or whether hospitals are properly located near elderly people. Calculating these service percentiles by county allows decision makers to easily identify regions where improvement is needed.

Introduction

The workflow for this script is broken down into three parts, each a separate ArcToolbox script:

  • Creating the service area-layer
  • Calculating the percent-coverage of each census block
  • Calculating the percent-coverage for a given demographic aggregated to a larger census level

The first part uses a network dataset and the locations of facilities, along with a user-specified service area (in distance or time), to generate a shapefile of the areas served.

The second part uses census block group geometry to calculate the area of the service area within each census block, as well as the area of each census block. These two variables are used to calculate the percentage of each census block that is within the specified distance of a facility.

The third part calculates the percentage of residents of a specified demographic variable within each county in a region that are serviced by a facility. Any census data variable can be used, including race, income, household type, education, and age.

The example included in this report calculates the county-by-county access of the total population, black residents, and single mothers to WIC centers in New York.