Modeling assumptions

Coordinate reference system

Use a projected CRS in meters. Buffers, grid resolution, route distance, and walking-speed conversion are not meaningful in longitude and latitude degrees.

Hazard, terrain, and road inputs

• Define the hazard zone for the question being asked; for tsunami modeling, distinguish the land-only origin zone from the escape boundary.
• Confirm the digital elevation model sign convention before using land and water thresholds. Do not assume every source uses positive values for land.
• Review road attributes and remove unsuitable features such as piers or routes that are not usable by pedestrians.

Buffers and origin density

road_buffer_m controls how far movement can extend from the road centerline. escape_buffer_m provides local access around candidate escape points. grid_resolution controls the sampling density of origins; finer grids increase runtime and should be justified by the terrain and road data resolution.

Conductance and least-cost paths

make_conductance_surface() uses a slope-based conductance surface from leastcostpath. The following arguments affect route geometry rather than just the final time conversion:

run_evacpath(
  ...,
  lcp_cost_function = "tobler",
  lcp_neighbours = 16,
  lcp_crit_slope = 12,
  lcp_max_slope = NULL
)

walking_speed_mps converts modeled route distance into time. It should be set to the population and planning scenario of interest.

The compact packaged run below shows the distinction: slower walking changes time conversion, while a different routing neighbourhood can also change modeled distance and route geometry.

Output clipping

clip_mode = "hazard" maps the time surface across the full hazard zone. "road_hazard" limits output to the road-buffer area, "hazard_plus_roads" retains both, and "none" leaves the Voronoi output unclipped. Choose the mode that matches the intended map interpretation.