How to align and avoid overlapping of multiple legends that are created separately and then added to the plots?

Question

I am trying to create a plot that combines 2 separate legends and a grid of multiple plots. The issue I'm having is I'm finding it difficult to align the legends so they are visible and not overlapping. hopefully the example below will explain what I mean.

To begin I am going to create 2 plots. In these two plots I am only interested in the legends, and I am discarding the actual plot (so please ignore the actual plots in these two plots). To get just the legend I am using the cowplot package.

library(ggplot2)
library(cowplot)
# -------------------------------------------------------------------------
# plot 1 ------------------------------------------------------------------

# create fake data
dfLegend_1 <- data.frame(x = LETTERS[1:10], y = c(1:10))
# set colours
pointColours <- c(A = "#F5736A", B = "#D58D00", C = "#A0A300",
                  D = "#36B300", E = "#00BC7B", F = "#00BCC2",
                  G = "#00ADF4", H = "#928DFF", I = "#E568F0",
                  J = "#808080")

# plot
ggLegend_1 <- ggplot(dfLegend_1, aes(x=x, y=y))+
  geom_point(aes(fill = pointColours), shape = 22, size = 10) +
  scale_fill_manual(values = unname(pointColours),
                    label = names(pointColours),
                    name = 'Variable') +
  theme(legend.key.size = unit(0.5, "cm")) +
  theme_void()

# get legend
legend_1 <- get_legend(ggLegend_1)


# -------------------------------------------------------------------------
# plot 2 ------------------------------------------------------------------


# Create fake data
dflegend_2 <- data.frame(
  x = runif(100),
  y = runif(100),
  z2 = abs(rnorm(100))
)

# plot
ggLegend_2 <- ggplot(dflegend_2, aes(x=x, y = y))+
  geom_point(aes(color = z2), shape = 22, size = 10) +
  scale_color_gradientn(
    colours = rev(colorRampPalette(c('steelblue', '#f7fcfd', 'orange'))(5)),
    limits = c(0,10),
    name = 'Gradient',
    guide = guide_colorbar(
      frame.colour = "black",
      ticks.colour = "black"
    ))

# get legend
legend_2 <- get_legend(ggLegend_2)

Then I am creating many plots (in this example, I am creating 20 individual plots) and plotting them on a grid:

# create data
dfGrid <- data.frame(x = rnorm(10), y = rnorm(10))

# make a list of plots
plotList <- list()
for(i in 1:20){
  plotList[[i]] <- ggplot(dfGrid) +
    geom_ribbon(aes(x = x, ymin = min(y), ymax = 0), fill = "red", alpha = .5) +
    geom_ribbon(aes(x = x, ymin = min(0), ymax = max(y)), fill = "blue", alpha = .5) +
    theme_void()
}

# plot them on  a grid
gridFinal <- cowplot::plot_grid(plotlist = plotList)

Finally, I am joining the two legends together and adding them to the grid of many plots:

# add legends together into on single plot
legendFinal <- plot_grid(legend_2, legend_1, ncol = 1)

# plot everything on the same plot
plot_grid(gridFinal, legendFinal,  rel_widths = c(3, 1))

This results in something that looks like this:

As you can see, the legends overlap and are not very well spaced. I was wondering if there is any way to fit everything in whilst having the legends appropriately spaced and readable?

I should also note, that, in general, there can be any number of variables and any number of gridded plots.

Answer 1

One option to fix your issue would be to switch to patchwork to glue your plots and the legends together. Especially I make use of the design argument to assign more space to the Variable legend. However, you should be aware that legends are much less flexible compared to plots, i.e. the size of legends is in absolute units and will not adjust to the available space. Hence, I'm not sure whether my solution will fit your desire for a "one-size-fits-all" approach.

library(patchwork)

design <- 
"
ABCDEU
FGHIJV
KLMNOV
PQRSTV
"

plotList2 <- c(plotList, list(legend_2, legend_1))

wrap_plots(plotList2) +
  plot_layout(design = design)

Answer 2

One way to avoid this is to add align = "v" argument in plot_grid() function, here is the result:

Answer 3

Based on the bold assumption that the colors in your legend actually represent something shown in the plot, may I suggest a completely different approach to the problem. Instead of awkwardly creating completely unrelated legends, use ggplot's automatic legend creation that will correctly map the legends to your plot aesthetics. I wonder what the color gradient is for, but you can create one for example simply with a fake geom layer. (Im using geom_point(shape = NA)).

This requires you to correctly map your groups (e.g., A/B/C, etc.) to your data. Having done that will allow you to only call geom_ribbon once.

I am then using patchwork to combine your plots and you can collect the guides. This requires all guides (legends) to be exactly the same. Which you ensure by specifying the limits within the scale_ functions.

Better, however, to use facets. This could be achieved by binding the presumed several data frames and using the origin as an ID for faceting.

The ribbons look a bit different because I am actually plotting the ribbons that correspond to y<0 and y>0. Otherwise, I thought having x would be pointless. Can obviously also changed to fill the entire x limits.

library(ggplot2)
library(dplyr)
library(patchwork)

pointColours <- c(
  A = "#F5736A", B = "#D58D00", C = "#A0A300",
  D = "#36B300", E = "#00BC7B", F = "#00BCC2",
  G = "#00ADF4", H = "#928DFF", I = "#E568F0",
  J = "#808080"
)
set.seed(1)
dfGrid <- data.frame(x = rnorm(10), y = rnorm(10))

## assuming that your color mean something, and this something is represented in your legend,
## you need to map the aesthetic to your data. based on this assumption, this example
df_ribbon <-
  dfGrid %>%
  mutate(
    group = ifelse(y <= 0, pointColours["A"], pointColours["H"]),
    ## I find it better to define your ymin and ymax outside of ggplot
    ymin = ifelse(y <= 0, min(y), 0),
    ymax = ifelse(y > 0, max(y), 0)
  )

# ls_p <- rep(
rep(list(ggplot(df_ribbon) +
  ## use fill as an aesthetic
  geom_ribbon(aes(x = x, ymin = ymin, ymax = ymax, fill = I(group)), alpha = .5) +
  ## fake geom_layer
  geom_point(aes(x = min(x), y = min(y), color = y), shape = NA, na.rm = T) +
  scale_color_gradientn(
    colours = rev(colorRampPalette(c("steelblue", "#f7fcfd", "orange"))(5)),
    limits = c(0, 10),
    name = "Gradient",
    guide = guide_colorbar(
      frame.colour = "black",
      ticks.colour = "black"
    )
  ) +
  scale_fill_manual(
    values = unname(pointColours),
    label = names(pointColours),
    ## important to add limits
    limits = pointColours,
    name = "Variable"
  ) +
    theme_void()), 20) %>%
  ## now merge the legends
  patchwork::wrap_plots() +
  plot_layout(guide = "collect")