# Graph drawing with netplot

#### George G. Vega Yon

#### 2026-07-23

Some features:

1. Auto-scaling of vertices using sizes relative to the plotting device.
2. Embedded edge color mixer.
3. True curved edges drawing.
4. User-defined edge curvature.
5. Nicer vertex frame color.
6. Better use of space filling the plotting device.

# Introduction

    library(netplot)
    library(igraph)
    library(sna)
    library(ggraph)

    # We will use the UKfaculty data from the igraphdata package
    data("UKfaculty", package = "igraphdata")

    # With a fixed layout
    set.seed(225)
    l_ukf <- layout_with_fr(UKfaculty)

Since igraph and statnet do the plotting using base system graphics, we can’t put everything in the same device right away. Fortunately, the `gridGraphics` R package allows us to reproduce base graphics using the `grid` system, which, in combination with the function `gridExtra::grid.arrange` will let us put both base and grid graphics in the same page. First me write a func

    # Function to map base to grid
    map_base_to_grid <- function(fun) {
      gridGraphics::grid.echo(fun)
      grid::grid.grab()
    }

    # Mapping base to grid
    ig <- map_base_to_grid(function() plot(UKfaculty, main = "igraph"))
    nw <- map_base_to_grid(function() gplot(as.matrix(as_adj(UKfaculty)), coord = l_ukf, main = "sna"))
    #> Warning: `as_adj()` was deprecated in igraph 2.1.0.
    #> ℹ Please use `as_adjacency_matrix()` instead.
    #> This warning is displayed once per session.
    #> Call `lifecycle::last_lifecycle_warnings()` to see where this warning was
    #> generated.

    nplot(UKfaculty, layout = l_ukf)
    grid::grid.text("netplot", x = .05, y=.9)
    np <- grid::grid.grab()

Here is an example with `ggraph`

    ggraph::ggraph(UKfaculty, layout = l_ukf) +
      ggraph::geom_edge_arc() +
      ggraph::geom_node_point() +
      ggplot2::ggtitle("ggraph")

    gg <- grid::grid.grab()

    # Putting all together
    gridExtra::grid.arrange(ig, nw, gg, np, nrow=2, ncol=2)

Comparison of default `igraph`, `sna`, `ggraph`, and `netplot` default call. `nplot` fills completely the plotting area, and adjusts vertex size, edge width, and edge arrows’ size accordingly to the plotting area and plotting device.

# Multiple plots

To arrange multiple plots in the same page we can use the `grid.arrange` function from the `gridExtra` package

    x_igraph  <- sample_smallworld(1, 20, 4, .05)
    x_network <- intergraph::asNetwork(x_igraph)

    l <- layout_nicely(x_igraph)

    # Putting two plots in the same page (one using igraph and the other network)
    gridExtra::grid.arrange(
      nplot(x_igraph, layout = l),
      nplot(x_network, layout = l), ncol=2, nrow=1
    )

# Nodes

    gridExtra::grid.arrange(
      nplot(UKfaculty, layout = l_ukf,
            vertex.size = rep(.025, vcount(UKfaculty)),
            vertex.size.range = NULL),
      nplot(UKfaculty, layout = l_ukf, vertex.size.range = c(.01, .025)),
      nplot(UKfaculty, layout = l_ukf, vertex.size.range = c(.01, .025, 4)),
      nplot(UKfaculty, layout = l_ukf, vertex.size.range = c(.02, .05, 4)),
      ncol=2, nrow=2
    )

Modifying `vertex.size.range`: use `NULL` to keep the supplied vertex sizes unchanged.

    nplot(make_ring(5), vertex.nsides = 2:6,
          vertex.size.range = c(.1,.1),
          edge.curvature = 0)

Number of sides for node drawing.

# Edges

    set.seed(12233)

    x <- sample_smallworld(1, size = 10, nei = 2, .1)
    l <- layout_with_fr(x)

    gridExtra::grid.arrange(
      nplot(
        x, layout          = l,
        edge.color        = ~ego(mix=0, alpha = .1, col="black") + alter(mix=1),
        vertex.size.range = c(.05,.1)
        ),
      nplot(
        x, layout          = l,
        edge.color        = ~ego(mix=.5, alpha = .1, col="black") + alter(mix=.5),
        vertex.size.range = c(.05,.1)
        ),
      nplot(
        x, layout          = l,
        edge.color        = ~ego(mix=1, alpha = .1, col="black") + alter(mix=0),
        vertex.size.range = c(.05,.1)
        ),
      ncol=3, nrow=1
    )

Modifying `edge.color.mix`: Each figure shows a different parameter for the edge color mixer. From left to right, (a) colors the edges as alter, (b) mixes ego and alter’s colors, and (c) only uses ego

    gridExtra::grid.arrange(
      nplot(x, layout = l, edge.curvature = 0, vertex.size.range = c(.05,.1)),
      nplot(x, layout = l, edge.curvature = pi/2, vertex.size.range = c(.05,.1)),
      nplot(x, layout = l, edge.curvature = pi, vertex.size.range = c(.05,.1)),
      ncol = 3, nrow=1
    )

Modifying `edge.curvature`: Each figure shows a different parameter for the edge curvature. From left to right, (a) straight edges, (b) the edge between ego and alter is an arc that measures \(\pi/2\) radians (90 degree), and (c) the edge as an arc between ego and alter that measures \(\pi\) radians (180 degrees).

    gridExtra::grid.arrange(
      nplot(x, layout = l, edge.line.breaks=3),
      nplot(x, layout = l, edge.line.lty = 2, edge.line.breaks=10),
      nplot(x, layout = l, edge.line.lty = 3, edge.line.breaks=10),
      nplot(x, layout = l, edge.line.lty = 4, edge.line.breaks=10),
      nrow=2, ncol=2
    )

Changing the number of breaks in the edge (arc) and the type of line to be drawn.

## Edge width

The `edge.width` parameter controls the relative width of each edge. Values are normalized and mapped to the range `[min, max]` specified by `edge.width.range` (in points). For `nplot.igraph`, this defaults to the `"weight"` edge attribute when present. Use `edge.width.range = NULL` to keep supplied widths unchanged.

    set.seed(1)
    x_w <- make_ring(8)

    # Assign varying edge weights
    E(x_w)$weight <- c(1, 3, 1, 5, 2, 4, 1, 6)
    l_w <- layout_in_circle(x_w)

    gridExtra::grid.arrange(
      nplot(x_w, layout = l_w, skip.arrows = TRUE,
            vertex.size.range = c(.05, .05),
            edge.width = 1,
            edge.width.range = c(1, 2)),
      nplot(x_w, layout = l_w, skip.arrows = TRUE,
            vertex.size.range = c(.05, .05),
            edge.width = E(x_w)$weight,
            edge.width.range = c(1, 2)),
      nplot(x_w, layout = l_w, skip.arrows = TRUE,
            vertex.size.range = c(.05, .05),
            edge.width = E(x_w)$weight,
            edge.width.range = NULL),
      ncol = 3, nrow = 1
    )

Effect of `edge.width` and `edge.width.range`. Left: uniform width. Middle: weights mapped to 1–2 pt. Right: raw weights with `edge.width.range = NULL`.

You can also modify edge widths after the plot has been created using `set_edge_gpar()`:

    g <- nplot(x_w, layout = l_w, skip.arrows = TRUE,
               vertex.size.range = c(.05, .05))

    gridExtra::grid.arrange(
      set_edge_gpar(g, element = "line", lwd = 1),
      set_edge_gpar(g, element = "line", lwd = 4),
      ncol = 2
    )

Using `set_edge_gpar()` to change edge widths after plotting. Left: all edges set to 1 pt. Right: all edges set to 4 pt.