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Compute origin-destination flow lines

Source: R/flow-lines.R
flow_lines.Rd

flow_lines() creates sf line geometries joining origin and destination locations. Lines can be straight or curved trajectories.

Usage

flow_lines(
  flows,
  locations,
  from,
  to,
  value = NULL,
  id,
  group = NULL,
  lon = NULL,
  lat = NULL,
  input_crs = 4326,
  crs = NULL,
  drop_self = TRUE,
  flow_curvature = 0,
  flow_n = 30
)

Arguments

flows

A data frame containing origin-destination pairs.

locations

A data frame or sf object containing one or more rows per location. Repeated locations are reduced to the first geometry per id.

from, to

Unquoted columns in flows identifying origin and destination ids.

value

Optional unquoted numeric column in flows used as flow value. If omitted, each flow receives value 1.

id

Unquoted location id column in locations.

group

Optional unquoted column in flows used to group or colour flow lines.

lon, lat

Unquoted longitude and latitude columns in locations. Required when locations is not an sf object.

input_crs

Coordinate reference system for lon and lat, or for an sf object with missing CRS. Defaults to EPSG:4326.

crs

Target projected CRS. If NULL, a projected CRS is selected from locations or an estimated UTM zone.

drop_self

Should self-flows be removed?

flow_curvature

Numeric curvature for trajectory lines. Use 0 for straight lines, positive values for one bend direction, and negative values for the opposite direction.

flow_n

Number of points used to approximate each curved trajectory.

Value

An sf object with one line per retained flow.

Examples

locations <- data.frame(
  place = c("A", "B"),
  lon = c(-71.3, -71.1),
  lat = c(46.75, 46.85)
)
flows <- data.frame(from = "A", to = "B", trips = 15)

lines <- flow_lines(
  flows,
  locations,
  from,
  to,
  trips,
  place,
  lon = lon,
  lat = lat
)
plot(lines["value"])