ggplot无法同时设置scale_size_continuous（）和scale_size（）

Question

我正在尝试为尺寸美学编辑图例，并为该美学设置比例尺尺寸，但似乎不能同时做到。

以下是步骤：

#create the map  
library(ggplot2)
world <- broders("world")

#generate a dataframe of geolocated data with attributes
points <- data.frame(lat = seq(0, 50, 10), 
                         lon = seq(0, 50, 10),
                         type = c("y", "n", "y", "n", "y", "n"), 
                         impact.x.r = seq(0, 50, 10))
points
lat lon type impact.x.r
1   0   0    y          0
2  10  10    n         10
3  20  20    y         20
4  30  30    n         30
5  40  40    y         40
6  50  50    n         50

然后我在ggplot中映射点-一切正常：

ggplot() + 
  world + 
  geom_point(data = points, aes(x = lon, y = lat, col = type, size = impact.x.r)) + 
  scale_color_discrete(name = "types of birds", breaks = c("n","y"), labels = c("no", "yes")) +
  scale_size_continuous(name = "impact")

但是，一旦我尝试使用+ scale_size()设置比例尺大小，就会出现错误。我也失去了为尺寸美学传奇制作的格式：

ggplot() + 
  world + 
  geom_point(data = points, aes(x = lon, y = lat, col = type, size = impact.x.r)) + 
  scale_color_discrete(name = "types of birds", breaks = c("n","y"), labels = c("no", "yes")) +
  scale_size_continuous(name = "impact") + 
  scale_size(range = c(0,15))

Scale for 'size' is already present. Adding another scale for 'size', which
will replace the existing scale.

如果我切换了scale_size_continuous()和scale_size()的呼叫顺序，我仍然会收到错误消息。这样一来，我就可以保留格式，但会丢失缩放比例的大小：

ggplot() + 
  world + 
  geom_point(data = points, aes(x = lon, y = lat, col = type, size = impact.x.r)) + 
  scale_color_discrete(name = "types of birds", breaks = c("n","y"), labels = c("no", "yes")) +
  scale_size(range = c(0,15)) +
  scale_size_continuous(name = "impact")
 Scale for 'size' is already present. Adding another scale for 'size', which
will replace the existing scale.    

因此它使用了对scale_size的最后一次调用...

但是我该如何修改图例以增加尺寸美感，并将scale_size设置为适合我的地图的尺寸​​？