r - 如何在r中的国家 map 上绘制位置点？

Question

我已经为我的特定问题搜索了很多，但找不到解决方案。虽然，我认为它很容易解决，但我是 r 的新手。

我想做什么:我想绘制一张黑白的印度 map 。我想用点和相应的名称绘制我访问过的所有地方。我设法用下面的代码完成了所有这些。

我的问题:如何以更简单的方式编写代码来绘制访问过的地方？我不想创建像 visit.x 这样的所有变量和 visit.y .此外，我必须为每个地方编写 geom_point 的代码。和 geom_text .当我试图一次绘制多个地方时，例如

visited <- c("New Delhi", "Rishikesh")

然后我收到错误消息“美学必须是长度为 1 或与数据相同”。

我的问题:如何将所有访问过的地方存储在一个变量中并在一次运行中绘制它？像这样我只需要一行 geom_point而不是我想绘制的每个地方。

#Load required packages
library(maps)
library(ggmap)
library(ggplot2)

#Dataframe with country relevant information
map <- fortify(map(fill = T, plot = F, region = "India"))

#Places I want to mark on the map
visited <- c("New Delhi")
visited2 <- c("Rishikesh")
visited3 <- c("Agra")

#Extracting long / lat of the places
visit.x <- geocode(visited)$lon
visit.y <- geocode(visited)$lat
visit.x2 <- geocode(visited2)$lon
visit.y2 <- geocode(visited2)$lat
visit.x3 <- geocode(visited3)$lon
visit.y3 <- geocode(visited3)$lat

#Defining font
font = c("Courier")
font.size = 3

#Specifing the look of the map with ggplot2
map_india <- ggplot(data = map, aes(x = long, y = lat, group = group)) +
    geom_polygon(fill = "white") +
    geom_path(colour = "black") +
    theme(panel.background = element_rect(fill = "#000000"),
          panel.grid.major = element_blank(),
          panel.grid.minor = element_blank(),
          axis.ticks = element_blank(),
          axis.text.y = element_blank(),
          axis.text.x = element_blank(),
          axis.title.x = element_blank(),
          axis.title.y = element_blank())

#Plotting the places I want on the map with labels
map_india <- map_india + 
    geom_point(aes(x = visit.x, y = visit.y)) +
    geom_text(data = NULL, x = visit.x - 1, y = visit.y + 0.2, label = "New Delhi", size = font.size, family = font) +
    geom_point(aes(x = visit.x2, y = visit.y2)) +
    geom_text(data = NULL, x = visit.x2 - 1, y = visit.y2 + 0.2, label = "Rishikesh", size = font.size, family = font) +
    geom_point(aes(x = visit.x3, y = visit.y3)) +
    geom_text(data = NULL, x = visit.x3, y = visit.y3 + 0.5, label = "Agra", size = font.size, family = font) +
    coord_fixed(0.8)

#Creating pdf
pdf("India.pdf", height = 11.69, width = 16.53)
print(map_india)
dev.off()

Answer 1

正如@hrbrmstr 在上面的评论中所建议的那样，ggplot2 旨在与 data.frames 一起使用，因此最好将您的数据始终保持在一个中。这样做实际上也大大简化了代码:

library(tidyverse)    # for ggplot2 and `%>%`
library(ggmap)
library(ggrepel)    # for geom_text_repel, though adjust overlaps manually if you prefer

cities <- data_frame(city = c("New Delhi", "Rishikesh", "Agra")) %>%    # start data.frame
        mutate_geocode(city)    # use ggmap function to add lon/lat columns

cities
#> # A tibble: 3 × 3
#>        city      lon      lat
#>       <chr>    <dbl>    <dbl>
#> 1 New Delhi 77.20902 28.61394
#> 2 Rishikesh 78.26761 30.08693
#> 3      Agra 78.00807 27.17667

box <- geocode('India', output = 'more')    # get lon/lat for bounding box

box
#>        lon      lat    type     loctype address   north    south     east
#> 1 78.96288 20.59368 country approximate   india 35.5087 6.753516 97.39556
#>       west country
#> 1 68.16289   India

get_stamenmap(bbox = c(left = box$west,    # get background tiles, set bounding box
                       bottom = box$south, 
                       right = box$east, 
                       top = box$north),
              maptype = 'toner-background',    # set map style
              zoom = 5) %>% 
    ggmap(extent = 'device') +    # note switch from %>% to + as moves to ggplot
    geom_point(aes(x = lon, y = lat), data = cities) +    # add points
    geom_text_repel(aes(x = lon, y = lat, label = city), data = cities)    # add labels

随心所欲地调整。