Legend for geospatial polygons with pattern - R

Question

I need to plot a map where different regions are filled with patterns rather than colors, so it can be printed black-and-white.

This post has a solution which works well for me: Fill Geospatial polygons with pattern - R

However, I cannot manage to add the legend with the patterns.

Here is what I've tried, based on the solution to the question in the link above, but I don't know what to pass to the fill argument within legend().

par(mar=c(1.1, 9.1, 1.1, 1.1), xpd=TRUE)

plot(bosnia,density=c(5,10,15)[bosnia$group], angle=c(0,45,90)[bosnia$group])

legend("topleft", inset=c(-0.4,0), ncol = 1,
  legend = c("Serb", "Croat", "Moslem"), 
  fill = c(density=c(100, 18, 30, 10, 45, 75, 22)[bosnia$group]),
  bg = "white")

How can I add a legend that fits this type of plot?

Ben · Accepted Answer · 2019-09-12T19:24:01.673

I think you do not need to use fill - instead include density and angle as below. Would set the legend to correspond to levels in your bosnia$group factor. In addition, increased density to 10, 15, and 20 and increased size (cex) for clarity.

par(mar=c(1.1, 9.1, 1.1, 1.1), xpd=TRUE)

plot(bosnia,density=c(10,15,20)[bosnia$group], angle=c(0,45,90)[bosnia$group])

legend("topleft", inset=c(-0.4,0), ncol = 1,
       legend = levels(bosnia$group), 
       density = c(10, 15, 20),
       angle = c(0, 45, 90),
       cex = 1.5,
       bg = "white")

Update: If you wish to increase just the size of the boxes in the legend, but not the text, you will need to create a revised legend function.

As mentioned in the comment, copy/paste the legend function (type legend in the console, copy and paste to editor), and rename new function something like legend_large_box:

legend_large_box <- function (x, y = NULL, legend, fill = NULL, col = par("col"), 
          border = "black", lty, lwd, pch, angle = 45, density = NULL, 
          bty = "o", bg = par("bg"), box.lwd = par("lwd"), 
          box.lty = par("lty"), box.col = par("fg"), pt.bg = NA, 
          cex = 1, pt.cex = cex, pt.lwd = lwd, xjust = 0, yjust = 1, 
          x.intersp = 1, y.intersp = 1, adj = c(0, 0.5), text.width = NULL, 
          text.col = par("col"), text.font = NULL, merge = do.lines && 
            has.pch, trace = FALSE, plot = TRUE, ncol = 1, horiz = FALSE, 
          title = NULL, inset = 0, xpd, title.col = text.col, title.adj = 0.5, 
          seg.len = 2) 
{...

In your example, fill is not included in the statement, so the lines you need to change for the larger box in this particular plot are:

xbox <- xc * 0.8
ybox <- yc * 0.5

Try something like 1.2 and 0.8 instead of 0.8 and 0.5.

Then call legend_large_box:

legend_large_box("topleft", inset=c(-0.4,0), ncol = 1,
       legend = levels(bosnia$group), 
       density = c(10, 15, 20),
       angle = c(0, 45, 90),
       bg = "white")

Thanks a lot! A follow up: with patterns, the default box size in the legend will often be too small. Is there a way to increase the size of the boxes, without increasing the whole legend box and text (which `cex`does)? I've tried the second suggestion from [this post](https://grokbase.com/t/r/r-help/118ndd7enr/r-increase-the-size-of-the-boxes-but-not-the-text-in-a-legend), i.e., altering the `legend` function. But changing `points2(x1, y1, pch = pch[ok], col = col[ok], cex = pt.cex[ok]` to `points2(x1, y1, pch = pch[ok], col = col[ok], cex = pt.cex[ok]+1.5`, as suggested there didn't do it. — Isabel, Sep 12 '19 at 10:29
Glad it was helpful. See edits to answer above regarding the larger box in the legend. — Ben, Sep 12 '19 at 19:24

Legend for geospatial polygons with pattern - R

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