在 map ggplot2/r 上创建点时出现问题

Question

I have a data set of UK earthquakes that I want to plot by location on a map. (Hopefully I then want to change the size to be representative of the magnitude). I have made a map of the uk using ggmap, but I am struggling to then add the points to a map.

I however keep getting 2 errors, and cannot plot my points on the map. The errors are either - Error: Aesthetics must be either length 1 or the same as the data (990): x, y or - Error in FUN(X[[i]], ...): object 'group' not found depending on how I try to plot the points.

this is what I have so far:

table <- data.frame(long2, lat2, mag1)
table

 long2  lat2 mag1
1  -2.62 52.84  1.9
2   1.94 57.03  4.2
3  -0.24 51.16  0.6
4  -2.34 53.34  0.8
5  -3.16 55.73  2.0
6  -0.24 51.16  1.0
7  -4.11 53.03  1.5
8  -0.24 51.16  0.2
9  -0.24 51.16  1.1
10 -5.70 57.08  1.6
11 -2.40 53.00  1.4
12 -1.19 53.35  1.2
13 -1.02 53.84  1.7
14 -4.24 52.62  0.8
15 -3.23 54.24  0.3
16 -2.06 52.62  1.0
17  1.63 54.96  1.7
18 -5.24 56.05  0.7
19 -5.86 55.84  1.3
20 -3.22 54.23  0.3
21 -0.24 51.16 -1.4
22 -0.24 51.16 -0.7
23 -4.01 55.92  0.3
24 -5.18 50.08  2.3
25 -1.95 54.44  1.0

library(ggplot2)
library(maps)

w <- map_data("world", region = "uk")

uk <- ggplot(data = w, aes(x = long, y = lat, group=group)) + geom_polygon(fill = "seagreen2", colour="white") + coord_map()
uk + geom_point(data=table, aes(x=long2, y=lat2, colour="red", size=2), position="jitter", alpha=I(0.5))

Is it the way I have built my map, or how I am plotting my points? And how do I fix it?

Answer 1

I've made three changes to your code, and one or more of them solved the problems you were having. I'm not sure exactly which—feel free to experiment!

1. I named your data pdat (point data) instead of table . table is the name of a built-in R function, and it's best to avoid using it as a variable name.
2. I have placed both data= expressions inside the geom function that needs that data (instead of placing the data= and aes() inside the initial ggplot() call.) When I use two or more data.frames in a single plot, I do this defensively and find that it avoids many problems.
3. I have moved colour="red" and size=2 outside of the aes() function. aes() is used to create an association between a column in your data.frame and a visual attribute of the plot. Anything that's not a name of a column doesn't belong inside aes() .

---

# Load data.

pdat <- read.table(header=TRUE,
text="long2  lat2 mag1
1  -2.62 52.84  1.9
2   1.94 57.03  4.2
3  -0.24 51.16  0.6
4  -2.34 53.34  0.8
5  -3.16 55.73  2.0
6  -0.24 51.16  1.0
7  -4.11 53.03  1.5
8  -0.24 51.16  0.2
9  -0.24 51.16  1.1
10 -5.70 57.08  1.6
11 -2.40 53.00  1.4
12 -1.19 53.35  1.2
13 -1.02 53.84  1.7
14 -4.24 52.62  0.8
15 -3.23 54.24  0.3
16 -2.06 52.62  1.0
17  1.63 54.96  1.7
18 -5.24 56.05  0.7
19 -5.86 55.84  1.3
20 -3.22 54.23  0.3
21 -0.24 51.16 -1.4
22 -0.24 51.16 -0.7
23 -4.01 55.92  0.3
24 -5.18 50.08  2.3
25 -1.95 54.44  1.0")

---

library(ggplot2)
library(maps)

w <- map_data("world", region = "uk")

uk <- ggplot() + 
      geom_polygon(data = w, 
                   aes(x = long, y = lat, group = group),
                   fill = "seagreen2", colour = "white") + 
      coord_map() + 
      geom_point(data = pdat, 
                 aes(x = long2, y = lat2), 
                 colour = "red", size = 2, 
                 position = "jitter", alpha = 0.5)

ggsave("map.png", plot=uk, height=4, width=6, dpi=150)