Remove extra space and ring at the edge of a polar plot

Question

I have a polar plot in ggplot2 that I am getting pretty close in finishing (fairly simple plot). I have been able to get assistance in removing the rectangular boarder but not I need to remove the extra space between the last range contour and the ring around the plot that has the azimuth labels on it. I would like for the bounds of this plot to be at 15,000... not 15,214 (I made that number up). Thanks for any help.

The code to generate the plot is below:

# Load needed Libraries ---------------------------------------------------

library(ggplot2)

# Generate Fake Data ------------------------------------------------------

N    = 25
bng  = runif(N, min =  0, max = 360)
rng  = rlnorm(N, meanlog = 9, sdlog = 1)
det  = runif(N, min = 0, max = 1) >= 0.5

det  = factor(det)

data = data.frame(bng, rng, det)

# Generate the Plot -------------------------------------------------------

plot = ggplot(data) + theme_bw() +
  geom_point(aes(x = bng, y = rng, color = det), size = 5, alpha = 0.7) +
  scale_x_continuous(limits = c(0,360), expand = c(0,0), breaks = seq(0,360-1, by=45)) +
  scale_y_continuous(limits = c(0,15000), breaks = seq(0,15000, by = 3000)) +
  coord_polar(theta = 'x', start = 0, direction = 1) +
  theme(legend.key = element_blank()) +
  theme(panel.border = element_blank(), axis.ticks = element_blank(), axis.text.y = element_blank()) +
  labs(x = '', y = '') +
  scale_color_manual(name = '', values = c('red', 'black'), breaks = c(FALSE, TRUE), labels = c('Not Detected', 'Detected'))
plot

Answer 1

The extra space is generated by the outermost circle of a panel.grid. The grid is added by default in the theme you have used (and in most other ggplot themes; default settings here)

Thus, remove panel.grid in theme. You might then create an own grid, according to taste, using e.g. geom_hline and geom_vline. Here I used the breaks you had specified in scale_x and _y as intercepts. I picked line colour and size from default panel.grid.major in theme_bw.

ggplot(data = df) +
  geom_point(aes(x = bng, y = rng, color = det), size = 5, alpha = 0.7) +
  geom_hline(yintercept = seq(0, 15000, by = 3000), colour = "grey90", size = 0.2) +
  geom_vline(xintercept = seq(0, 360-1, by = 45), colour = "grey90", size = 0.2) +
  coord_polar(theta = 'x', start = 0, direction = 1) +
  labs(x = '', y = '') +
  scale_color_manual(name = '',
                     values = c('red', 'black'),
                     breaks = c(FALSE, TRUE),
                     labels = c('Not Detected', 'Detected')) +
  scale_x_continuous(limits = c(0, 360), expand = c(0, 0), breaks = seq(0, 360-1, by = 45)) +
  scale_y_continuous(limits = c(0, 15000), breaks = seq(0, 15000, by = 3000)) +
  theme_bw() +
  theme(panel.border = element_blank(),
        legend.key = element_blank(),
        axis.ticks = element_blank(),
        axis.text.y = element_blank(),
        panel.grid  = element_blank())