spax is an R package designed for advanced spatial accessibility analysis, focusing on Two-Step Floating Catchment Area (2SFCA) methods and their derivatives. The package offers a fresh perspective on spatial accessibility through its raster-based computational approach and modular design.
Features
- Computational Simplicity: Raster-based operations translate complex spatial relationships into simple matrix calculations
- Modular Design: Functions work like LEGO bricks - mix and match components to build custom analysis workflows
- Complex Demand Handling: Support for continuous population surfaces, letting you work with high-resolution demand data
- Monte Carlo Integration: Built-in tools for uncertainty analysis and stochastic demand modeling
Installation
You can install the development version of spax from GitHub with:
# install.packages("pak")
pak::pak("Songyosr/spax")Example
Here’s how spax’s modular design works in practice, analyzing healthcare accessibility in Thailand’s Region 12:
library(spax)
library(terra)
library(sf)
# Load example data (already included in package)
pop <- read_spax_example("u5pd.tif") # Under-5 population density
distance <- read_spax_example("hos_iscr.tif") # Travel times
hospitals <- hc12_hos # Hospital locations and capacity
# Calculate accessibility using Enhanced 2SFCA
result <- spax_e2sfca(
demand = pop, # Population density
supply = hospitals |> st_drop_geometry(), # Hospital capacity
distance = distance, # Travel times
decay_params = list(
method = "gaussian",
sigma = 30 # 30-minute characteristic distance
),
demand_normalize = "standard", # Prevent demand inflation
id_col = "id",
supply_cols = c("s_doc", "s_nurse") # Analyze both doctors and nurses
)
# Plot results
plot(result, main = c("Access to Doctors", "Access to Nurses"),
fun = function() lines(bound0)
)
result
#> Spatial Accessibility Analysis (E2SFCA)
#>
#> Spatial Properties:
#> - Resolution: 520.404 x 520.404
#> - Dimensions: 509 x 647
#>
#> Measures: 2
#> - s_doc
#> - s_nurse
#>
#> Facilities: 77
#>
#> Parameters:
#> - Decay function: gaussian (sigma = 30)
#> - Demand normalization: standard
summary(result)
#>
#> Summary of Spatial Accessibility Analysis (E2SFCA)
#> ---------------------------------------------
#>
#> Accessibility Measures:
#>
#> s_doc:
#> Range: 2.14e-10 to 0.1818
#> Mean (SD): 0.06002 (0.03767)
#> Quantiles:
#> Min.: 2.14e-10
#>
#> Coverage: 33.2% (109362 of 329323 cells)
#>
#> s_nurse:
#> Range: 4.172e-10 to 0.2736
#> Mean (SD): 0.1066 (0.06332)
#> Quantiles:
#> Min.: 4.172e-10
#>
#> Coverage: 33.2% (109362 of 329323 cells)
#>
#> Facility Statistics:
#> -------------------
#> Total Facilities: 77
#>
#> s_doc:
#> Total Supply: 4669
#> Mean (SD): 60.64 (80.09)
#> Range: 0 to 522
#>
#> s_nurse:
#> Total Supply: 8125
#> Mean (SD): 105.5 (159.1)
#> Range: 0 to 973This example demonstrates key features of spax:
Working with continuous population surfaces (demand)
Handling multiple supply indicators simultaneously
Gaussian distance decay for more realistic accessibility modeling