1 R + leaflet 互联网制图

1.1 基本用法

通过 leaflet() 初始化一个地图.
利用以下函数 (e.g. addTiles, addMarkers, addPolygons) 来添加图层.
重复第二步完成你想要的设置.
输出地图.

一个简单的例子：

library(leaflet)
# library(magrittr)

m <- leaflet() %>%
  addTiles() %>%  # Add default OpenStreetMap map tiles
  addMarkers(lng=116.67498, lat=40.40652, popup="The University of Chinese Academy of Sciences")
m  # Print the map

如果你对R中的管道操作（%>%）不熟悉，可以采用以下方式：

m <- leaflet()
m <- addTiles(m)
m <- addMarkers(m, lng=116.67498, lat=40.40652, popup="The University of Chinese Academy of Sciences")
m

leaflet中可以接受的输出数据包括以下几种：

From base R:
From the maps package:
- the data frame from returned from map()

1.2 数据输入

第一种：输入数据为经纬度坐标

lng/lat matrix
data frame with lng/lat columns

m <- leaflet() %>% addTiles()
df <- data.frame(
  lat = rnorm(100),
  lng = rnorm(100),
  size = runif(100, 5, 20),
  color = sample(colors(), 100)
)
m <- leaflet(df) %>% addTiles()
m %>% addCircleMarkers(radius = ~size, color = ~color, fill = FALSE)

## Assuming 'lng' and 'lat' are longitude and latitude, respectively

m %>% addCircleMarkers(radius = runif(100, 4, 10), color = c('red'))

## Assuming 'lng' and 'lat' are longitude and latitude, respectively

第二种：空间数据格式

sp package:

SpatialPoints[DataFrame]
Line/Lines
SpatialLines[DataFrame]
Polygon/Polygons
SpatialPolygons[DataFrame]

第三种：maps包中的数据

maps package:

the data frame from returned from map()

# install.packages("maps")
library(maps)
mapStates = map("state", fill = TRUE, plot = FALSE)
leaflet(data = mapStates) %>% addTiles() %>%
  addPolygons(fillColor = topo.colors(10, alpha = NULL), stroke = FALSE)

1.3 地图选择

1.3.1 第三方地图

leaflet支持多种类型的底图，包括Google Map，Openstreetmap等，默认为OSM的底图。也可以添加第三方的底图。

改变底图的函数：addProviderTiles(), 也可以通过改变leaflet-providers plugin来改变，更全面的例子见这里。

m <- leaflet() %>% setView(lng=116.67498, lat=40.40652, zoom = 12)
m %>% addTiles()

m %>% addProviderTiles(providers$Stamen.Toner)

m %>% addProviderTiles(providers$CartoDB.Positron)

m %>% addProviderTiles(providers$Esri.NatGeoWorldMap)

1.3.2 WMS Tiles

可以利用addWMSTiles()来添加WMS (Web Map Service) tiles。

The map below shows the Base Reflectivity (a measure of the intensity of precipitation occurring) using the WMS from the Iowa Environmental Mesonet:

leaflet() %>% addTiles() %>% setView(-93.65, 42.0285, zoom = 4) %>%
  addWMSTiles(
    "http://mesonet.agron.iastate.edu/cgi-bin/wms/nexrad/n0r.cgi",
    layers = "nexrad-n0r-900913",
    options = WMSTileOptions(format = "image/png", transparent = TRUE),
    attribution = "Weather data © 2012 IEM Nexrad"
  )

1.3.3 多种底图叠加

还可以通过设置透明色的方式，将多种底图进行叠加显示

m %>% addProviderTiles(providers$MtbMap) %>%
  addProviderTiles(providers$Stamen.TonerLines,
    options = providerTileOptions(opacity = 0.35)) %>%
  addProviderTiles(providers$Stamen.TonerLabels)

互联网地图学 — ex 2

Jianghao Wang

2017-12-10