Get started with evacpath

evacpath estimates road-constrained pedestrian distance to safety and converts that modeled distance into an evacuation-time surface. A practical workflow needs a hazard zone, a road or pathway network, an elevation raster, and a projected coordinate reference system (CRS) in meters.

Install and load

install.packages("evacpath")
library(evacpath)
library(terra)

Load the packaged example data

The package includes small example inputs for learning the workflow. They are not a substitute for local hazard, road, terrain, or evacuation-planning data.

dem <- rast(system.file("extdata/dem.tif", package = "evacpath"))
roads <- vect(system.file("extdata/rds.gpkg", package = "evacpath"))
inundation <- rast(system.file(
  "extdata/tsunami_inundation_depth.tif",
  package = "evacpath"
))

zones <- prepare_tsunami_zones(
  inundation = inundation,
  dem = dem,
  target_crs = "EPSG:32748"
)

The compact run used for the figures and summaries below is clipped to a small projected window. It uses 40 sampled road origins and 12 candidate safety exits.

Input	Example value
Coordinate reference system	EPSG:32748
Hazard-zone area (square km)	4.048
Road features	254
Candidate safety exits	12
Sampled road origins	40

Run the workflow

For a first pass, use a modest number of origins and destinations. Remove or raise those limits only after reviewing the input layers and assumptions.

result <- run_evacpath(
  hazard_zone = zones$hazard_zone,
  escape_zone = zones$escape_zone,
  roads = roads,
  dem = zones$dem,
  target_crs = "EPSG:32748",
  max_origins = 100,
  max_destinations = 25,
  walking_speed_mps = 1.22
)

Modeled evacuation time to safety for the compact packaged example.

The example summary is a description of the modeled road-origin results, not a measure of observed evacuation behavior.

Modeled output	Example value
Minimum modeled time (minutes)	0.31
Median modeled time (minutes)	10.09
Mean modeled time (minutes)	9.65
Maximum modeled time (minutes)	22.84
Origins	40.00
Destinations	12.00
Walking speed (m/s)	1.22

What you get back

run_evacpath() returns a named list. The main layers are summarized below so you can inspect or write only the outputs needed for the analysis.

Object	Purpose
hazard_zone	Land-only area used for evacuation origins and mapped output.
escape_points	Candidate safety exits identified at the selected escape boundary.
road_points	Sampled road-based origins used for least-cost calculations.
distance_points	Modeled distance to safety for sampled origins and zero-distance exits.
evac_polygons / time_grid	Polygonized modeled distance and time surface for map output.

Use result$evac_polygons, result$distance_points, result$time_grid, and result$escape_points for the mapped and point outputs. Run diagnose_evac_model() before interpreting a result to make coordinate-system, geometry, extent, and reachability checks explicit.