How can I use ggplot to merge maps of land without any water and contour plots, while also obscuring or filling in ocean areas?

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To merge maps of land without water and contour plots and remove the ocean areas, you can follow these steps:

1. Load the required libraries: ggplot2, maptools, and raster.

library(ggplot2)
library(maptools)
library(raster)

1. Load the shapefile containing the land data using the readShapePoly() function from the maptools package.

land <- readShapePoly("land.shp")

1. Load the contour plot data as a raster object using the raster() function from the raster package.

contours <- raster("elevation.tif")

1. Convert the raster object to a data frame using the fortify() function from the ggplot2 package.

contours.df <- fortify(contours)

1. Merge the land and contour plot data frames using the merge() function in R.

merged.df <- merge(land, contours.df, by = "id")

1. Create a ggplot object with the merged data frame.

ggplot(merged.df) +
  geom_polygon(aes(x = long, y = lat, group = group, fill = value)) +
  coord_equal() +
  theme_void()

1. Add a background layer with the ocean areas filled or obscured.

To obscure the ocean areas, you can add a layer with a polygon that covers the entire plot area with a color that matches your plot background. For example:

ggplot(merged.df) +
  geom_polygon(aes(x = long, y = lat, group = group, fill = value)) +
  coord_equal() +
  theme_void() +
  geom_polygon(data = world, aes(long, lat, group = group), fill = "white")

To fill in the ocean areas with a color, you can use the ggrepel package to create a layer with text labels that cover the ocean areas, and set the text color to match your plot background. For example:

library(ggrepel)

ggplot(merged.df) +
  geom_polygon(aes(x = long, y = lat, group = group, fill = value)) +
  coord_equal() +
  theme_void() +
  geom_text_repel(data = world, aes(long, lat, label = " "), size = 10, color = "white")