add_flowmap: Add a flow map to a ggplot

Description

Add a flow map to a ggplot

Usage

add_flowmap(
  p,
  flowdat = NULL,
  od = NULL,
  nodes = NULL,
  outline_linewidth = 0.01,
  alpha = 0.8,
  nodes_alpha = 0.8,
  outline_col = "black",
  k_nodes = NULL,
  node_buffer_factor = 1.2,
  node_radius_factor = 1,
  edge_offset_factor = 1,
  node_fill_factor = NULL,
  edge_width_factor = 1.2,
  arrow_point_angle = 45,
  add_legend = "none",
  legend_nudge_x = 0,
  legend_nudge_y = 0,
  legend_col = "gray"
)

Value

The ggplot with an additional polygon layer for the flow arrows and an additional polygon layer for the nodes

Arguments

p: The plot to which the flowmap should be added.
flowdat: Input dataframe. See details below.
od: As an alternative to flowdat, dataframe with the origin-destination pairs and the flow between them. Must contain the columns o, d, value. nodes must be provided as well. See details below.
nodes: As an alternative to flowdat, a dataframe with the nodes of the network. Must contain the columns name, x, y. See details below.
outline_linewidth: The linewidth of the outline of the arrows.
alpha: Opacity of the edges.
nodes_alpha: Opacity of the nodes.
outline_col: Color of the outline of the edges.
k_nodes: Number of clusters to group nodes into. If defined, nodes will be clustered hierarchically based on spatial proximity. By default, no clustering will be applied.
node_buffer_factor: Controls the distance between the nodes and the edges ( in multiple of the nodes' radii).
node_radius_factor: Controls the size of the nodes.
edge_offset_factor: Controls the distance between the parallel arrows.
node_fill_factor: Controls the downscaling of the fill of the nodes ( as to not outshine the edges ).
edge_width_factor: Controls the width of the edges.
arrow_point_angle: Controls the pointiness of the edges.
add_legend: Add a legend for width to the plot? Must be one of "none","bottom","top","left", or "right". (Experimental)
legend_nudge_x: Adjusts the horizontal position of the legend in map units.
legend_nudge_y: Adjusts the vertical position of the legend in map units.
legend_col: If add_legend, controls the color of the legend. Default is grey.

Author

Johannes Mast

Details

The function requires as inputs a dataframe flowdat which contains for every combination of two nodes a and b the coordinates of these nodes as well as the intensity of flow between those nodes in both directions (a to b, b to a). The dataframe should have the following columns:

id_a: The unique id of node a
id_b: The unique id of node b
xa: The x coordinate of node a
ya: The y coordinate of node a
xb: The x coordinate of node b
yb: The y coordinate of node b
flow_ab: The intensity of flow from node a to node b
flow_ba: The intensity of flow from node b to node a

Alternatively, the function can take as input a dataframe od which contains the origin-destination pairs and the flow between them. The dataframe should have the following columns:

o: The unique id of the origin node
d: The unique id of the destination node
value: The intensity of flow between the origin and destination

In this case, the function also requires a dataframe nodes which contains the coordinates of the nodes. The dataframe should have the following columns:

name: The unique id of the node
x: The x coordinate of the node
y: The y coordinate of the node

The function will impose coord_equal() on the ggplot.

Inspired by flowmap.gl.

Examples

Run this code

testdata <-
data.frame(
 id_a = c("X1","X2","X3","X3","X1"),
 id_b = c("X8","X7","X1","X8","X7"),
 xa = c(2,14,10,10,2),
 ya = c(6,10,9,9,6),
 xb = c(10,4,2,10,4),
 yb = c(4,10,6,4,10),
 flow_ab = c(2,1,1,1,1),
 flow_ba = c(5,1,1,1,2)
)
library(ggplot2)
plot <- ggplot()
plot |> add_flowmap(testdata)

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