使用ggplot2插入地图

Question

我只是想制作一个简单的研究区域地图，其中还包含我正在工作的州（北卡罗来纳州）的插图。我想将插图地图转换为grob对象，将其绘制在主要研究区域地图中，然后使用ggsave将地图保存为图像，pdf等。我正在使用shapefile作为我的实际地图，但我＆＃39 ; ll将向您展示我正在尝试使用map_data：

library(ggplot2)
library(ggmap)
library(maps)
library(mapdata)
library(gridExtra)
library(grid)

# get the NC data:
states <- map_data("state")
nc_df <- subset(states, region == "north carolina")

# study area map:
nc_base <- ggplot() + 
geom_polygon(data = nc_df, aes(x = long, y = lat, group = group), fill="grey", color="black") +
coord_fixed(xlim=c(-80, -77.5), ylim=c(33.5, 34.9), ratio = 1.3) +
theme_bw()
nc_base

# inset map:
insetmap<-ggplot() + 
geom_polygon(data = nc_df, aes(x = long, y = lat, group = group), fill="grey", color="black")  + # get the state border back on top
coord_fixed(ratio = 1.3) +
annotate(geom = "rect", ymax = 34.9, ymin = 33.5, xmax = -77.5, xmin = -80, colour = "red", fill = NA) +
ylab("") +
xlab("") +
theme_nothing()
insetmap

insetmap.grob <- ggplotGrob(insetmap)

final_map <- nc_base + annotation_custom(insetmap.grob, xmin=-79.5, xmax=-79, ymin=33.75, ymax=34)
final_map

当我运行脚本来生成最终地图时，只会生成研究区域地图。我想知道我是否错误地使用了ggplotGrob，或者是其他什么？我可能在其他地方读过，除非你在ggplot2中使用coord_cartesian函数（这里我使用的是coord_fixed），否则annotation_custom函数不起作用。如果是这种情况，我可以使用该功能进行类似放大，还是有另一个coord_函数可以放大我的学习区域地图？

谢谢， 杰

Answer 1

我经常做这种事情，并且发现grid :: viewport方法效果很好......虽然注意到在使用多个视口时不能使用ggsave，因为ggsave只会保存最后一个视口。 尝试：

nc_base <- ggplot() + 
  geom_polygon(data = nc_df, aes(x = long, y = lat, group = group), fill="grey", color="black") +
  coord_fixed(xlim=c(-80, -77.5), ylim=c(33.5, 34.9), ratio = 1.3) +
  theme_bw()
print(nc_base)

# inset map:
insetmap <- ggplot() + 
  geom_polygon(data = nc_df, aes(x = long, y = lat, group = group), fill="grey", color="black")  + # get the state border back on top
  coord_fixed(ratio = 1.3) +
  annotate(geom = "rect", ymax = 34.9, ymin = 33.5, xmax = -77.5, xmin = -80, colour = "red", fill = NA) +
  ylab("") +
  xlab("") + 
# used theme_inset instead of theme_nothing
  theme_inset()
print(insetmap)

# save where you want to with filename arg in png(). Currently saves 'map.png' to your working directory
# set resolution, width, height
png(filename = "map.png", width = 1150, height = 800, res = 300)
# create a viewport for inset
# vp_inset width/height arguments set the size of the inset; x and y arguments set the position (from 0 to 1) of the left, top corner of the inset along each axis (i.e. not map coordinates as you have in your annotation custom). You can adjust these as you see fit.
vp_inset <- grid::viewport(width = 0.35, height = 0.35, x = 0.2, y = 0.5, just = c("left", "top"))
print(nc_base)
print(insetmap, vp = vp_inset)
dev.off()