Skip to contents

Download and downscale a friction surface layer

Source: R/friction.R
friction.Rd

friction() retrieves a friction surface layer from the Malaria Atlas Project (MAP) database (Hay et al., 2006; Malaria Atlas Project, 2015, 2019) and optionally downscale it to the spatial resolution of the analysis using road network data from OpenStreetMap (n.d.) (OSM).

This function requires an active internet connection.

Usage

friction(
  bb_area,
  mode = "walk",
  dowscaling_model_type = "lm",
  res_output = 100,
  cache = FALSE,
  file = NULL
)

Arguments

bb_area

A sf boundary box object with the area of interest.

mode

(optional) A character string indicating the mode of transport. Options are "fastest" and "walk" (default = "walk").

  • For "fastest": The friction layer accounts for multiple modes of transport, including walking, cycling, driving, and public transport, and are based on the Malaria Atlas Project (2019) Global Travel Speed Friction Surface.

  • For "walk": The friction layer accounts only for walking speeds and is based on the Malaria Atlas Project (2015) Global Walking Only Friction Surface.

dowscaling_model_type

(optional) A character string indicating the type of model used for the spatial downscaling of the friction layer. Options are "lm" (linear model) and "rf" (random forest) (default: "lm").

res_output

(optional) A positive integerish number indicating the spatial resolution of the friction raster (and of the analysis), in meters. If the resolution is less than 1000, a spatial downscaling approach is used (default: 100).

cache

(optional) A logical flag indicating whether to cache the downloaded friction data for future use (default: TRUE).

file

(optional) A character string indicating the path to a local friction surface raster file. If provided, the function will use this file instead of downloading the friction data.

Value

An invisible list with the following elements:

  • friction_layer: A RasterLayer object with the friction surface layer.

  • transition_matrix: A TransitionLayer with the transition matrix for cost-distance calculations.

  • geocorrection_matrix: A TransitionLayer with the geocorrection matrix for accurate distance calculations.

References

Hay, S. I., & Snow, R. W. (2006). The Malaria Atlas Project: Developing global maps of malaria risk. PLOS Medicine, 3(12), e473. doi:10.1371/journal.pmed.0030473

Malaria Atlas Project. (2015). Friction surface: Global travel speed friction surface (Version 201501). https://data.malariaatlas.org/maps

Malaria Atlas Project. (2019). Friction surface: Global walking only friction surface (Version 202001). https://data.malariaatlas.org/maps

OpenStreetMap Foundation. (n.d.). OpenStreetMap [Computer software]. https://www.openstreetmap.org

See also

Other travel time functions: traveltime(), traveltime_plot(), traveltime_stats()

Examples

if (FALSE) { # \dontrun{
  naples_shape |> friction()
} # }