ggplot繪制map

R語言可以進行數(shù)據(jù)分析，也可以進行地圖繪制，而且非常簡潔，快速。
雖然Arcgis基于桌面可視化操作，能夠進行空間分析，但是唯一不足的就是操作步驟繁瑣而且一不小心，就要從頭再來，可重復性較低。

這篇文章主要講述如何利用R語言中的ggplot與sf繪制帶有指北針、圖列與標尺的地圖

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數(shù)據(jù)

我們下載非洲地區(qū)54個國家的圖層Afirca.json保存在本地。然后加載包去讀取。然后在ggplot中使用 geom_sf來簡單畫出非洲地區(qū)的輪廓

library(tidyverse)
library(sf)
library(ggspatial)
library(ggthemes)
# https://geojson-maps.ash.ms/
africa <- read_sf("africa.json")

# plot
africa %>% 
  ggplot() + 
  geom_sf()
 
# populations with colors
ggplot(africa) +
  geom_sf(aes(geometry = geometry, fill = pop_est))

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指北針

一張標準的地圖需要有比例尺，地圖及指北針，所以這次我們加上比例尺與指北針，通過ggspatial包，調(diào)用annotation_scale來增加比例尺。location = "bl"是調(diào)整比例尺位置， width_hint = 0.3調(diào)整比例的長度。
annotation_north_arrow則是用來添加指北針。style =north_arrow_nautical來更改指北針的類型，主要有north_arrow_orienteering；north_arrow_fancy_orienteering；north_arrow_minimal與north_arrow_nautical四種類型，其他參數(shù)可help(annotation_north_arrow)查看。

# with scales and north_arrow
ggplot(africa) +
  geom_sf(aes(geometry = geometry, fill = pop_est)) +
  annotation_scale(location = "bl", width_hint = 0.4) +
  annotation_north_arrow(location = "tr", which_north = "true", 
                         pad_x = unit(0.05, "in"), pad_y = unit(0.05, "in"),
                         style = north_arrow_nautical) 

屏幕快照 2020-06-29 上午1.37.08.png

背景調(diào)整

如果不喜歡有grid的背景，可以根據(jù)喜好，調(diào)節(jié)自己喜歡的背景
這里我們采用， theme_light()白色網(wǎng)格背景。更多背景設置，請見ggplot2 主題背景設置

# with blank themes
ggplot(africa) +
  geom_sf(aes(geometry = geometry, fill = pop_est)) +
  annotation_scale(location = "bl", width_hint = 0.4) +
  annotation_north_arrow(location = "tr", which_north = "true", 
                         pad_x = unit(0.05, "in"), pad_y = unit(0.05, "in"),
                         style = north_arrow_nautical) +
  theme_light()

屏幕快照 2020-06-29 上午1.48.33.png

圖例顏色

默認的圖例顏色是blue色調(diào)，我們可以根據(jù)
來更改紅色基準的色調(diào)。
legend 是默認的分段方式，我們可以根據(jù)需要設定成4分類，或者更改圖例的距離。

# with colors
ggplot(africa) +
  geom_sf(aes(geometry = geometry, fill = pop_est)) +
  scale_fill_gradientn(colours=brewer.pal(5,"Reds"))+
  annotation_scale(location = "bl", width_hint = 0.4) +
  annotation_north_arrow(location = "tr", which_north = "true", 
                         pad_x = unit(0.05, "in"), pad_y = unit(0.05, "in"),
                         style = north_arrow_nautical) +
  theme_light()

# for 4 categories
africa %>% mutate( new=cut(pop_est,b = 4)) %>% 
ggplot() +
  geom_sf(aes(geometry = geometry, fill = new)) +
  annotation_scale(location = "bl", width_hint = 0.4) +
  annotation_north_arrow(location = "tr", which_north = "true", 
                         pad_x = unit(0.05, "in"), pad_y = unit(0.05, "in"),
                         style = north_arrow_nautical) +
  theme_light()
  
 # set for sacles

my_breaks = c(0,3207562,10401245,18419935,20644434,149229090 )
ggplot(africa) +
  geom_sf(aes(geometry = geometry, fill = pop_est)) +
  scale_fill_gradient(name = "count", 
                        breaks = my_breaks, labels = my_breaks)
                        
#
ggplot(africa) +
  geom_sf(aes(geometry = geometry, fill = pop_est)) +
  scale_fill_gradient(name = "count", 
                        breaks = my_breaks, labels = my_breaks, guide="legend")
  

屏幕快照 2020-06-29 上午1.47.58.png

屏幕快照 2020-06-29 上午1.48.05.png

關于更多顏色設置ggplot2: Elegant Graphics for Data Analysis
legend分類legend and labels

參考

1. Geospatial Visualization
2. sf 與指北針
3. geocompkg | metapackage for the Gecomputation with R book
4. This repository contains the source for the book Geospatial Visualization.
5. Chapter 8: Making maps with R
6. ggplot2 主題背景設置