Accessibility Analysis

Overview

In spatial analysis, accessibility analysis quantifies how easily individuals or locations can reach essential services or destinations within a given area. It examines factors such as the distribution of the facility, transportation networks, socioeconomic factors, and population characteristics to identify areas with limited access. In urban health, accessibility analysis helps assess healthcare access within cities, informing decision-making for resource allocation and policy development to improve healthcare equity and population health outcomes.

Key Methods Within Accessibility Analysis

1. Isochrone Analysis

   Isochrone analysis is a spatial analysis technique used to visualise areas that can be reached within a specified travel time or distance from a given location, taking into account the road network or transportation links. It creates polygons on a map representing areas that can be reached within uniform intervals of time or distance, considering factors such as road conditions, speed limits, and traffic congestion. By incorporating the transportation network, isochrone analysis provides more accurate estimations of accessibility, helping to identify accessible regions and assess travel patterns and accessibility to services or facilities within a geographic area.

2. Two-Step Floating Catchment Area (2SFCA) Method

   The 2SFCA method developed by Luo and Wang [1, 2, 3], is a spatial analysis technique used to evaluate accessibility to various services such as healthcare facilities, within a defined geographic region. It involves two key steps: firstly, quantifying the supply of services within predetermined catchment areas; and secondly, calculating accessibility by aggregating the supply of service within these catchment areas relative to the demand for services from nearby populations.

   Enhanced versions of the 2SFCA method have been developed, including the Three-Step Floating Catchment Area (3SFCA) method, incorporating additional factors such as distance and travel impedance, facility capacity, and population characteristics to provide more nuanced insights into accessibility patterns. The choice between utilising different versions of the 2SFCA method or adopting the 3SFCA method depends on the specific use case and research objectives, highlighting the importance of tailoring the methodology to address the unique characteristics and requirements of each study context.

   Steps to Calculate Accessibility with 2SFCA

   Step 1 - Calculation of Supply:

   For each healthcare facility $i$, calculate the supply of healthcare services within its catchment area.

   $$H_i = \sum_{j\in\text A_i} P_j$$

   Where,

   $H_i$ is the number of healthcare facilities in unit $i$,

   $P_j$ is the population in unit $j$,

   $A_i$ is the catchment area of unit $i$.

   Step 2 - Calculation of Accessibility:

   For each location $j$, calculate the accessibility to healthcare services by aggregating the supply of services from nearby facilities.

   $$A_j = \sum_{i\in\text B_j} \frac{H_i}{D_{ij}}$$

   Where,

   $A_j$ is the accessibility to healthcare services at location $j$,

   $B_j$ is the set of facilities whose catchment areas intersect with location $j$,

   $D_{ij}$ is the distance or travel time between facility $i$ and location $j$.

   References

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   1. Wang F, Luo W: Assessing spatial and nonspatial factors for healthcare access: towards an integrated approach to defining health professional shortage areas. Health Place 2005, 11:131–146.

   2. Luo W, Wang F: Measures of spatial accessibility to health care in a GIS environment: synthesis and a case study in the Chicago region. Environ Plann B 2003, 30:865–884

   3. Luo W: Using a GIS-based floating catchment method to assess areas with shortage of physicians. Health Place 2004, 10:1–11.