title	author	date	output
互联网地图学 — ex 2	Jianghao Wang	`r Sys.Date()`	prettydoc::html_pretty theme highlight toc toc_depth number_sections architect github true 4 true

# R + leaflet 互联网制图 ## 基本用法 1. 通过 `leaflet()` 初始化一个地图. 2. 利用以下函数 (e.g. `addTiles`, `addMarkers`, `addPolygons`) 来添加图层. 3. 重复第二步完成你想要的设置. 4. 输出地图. 一个简单的例子： ```{r warning=FALSE} library(leaflet) # library(magrittr) m % 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： ```{r eval=FALSE} m % addTiles() df % addTiles() m %>% addCircleMarkers(radius = ~size, color = ~color, fill = FALSE) m %>% addCircleMarkers(radius = runif(100, 4, 10), color = c('red')) ``` **第二种：空间数据格式** [**sp** package](http://cran.rstudio.com/package=sp): - `SpatialPoints[DataFrame]` - `Line`/`Lines` - `SpatialLines[DataFrame]` - `Polygon`/`Polygons` - `SpatialPolygons[DataFrame]` **第三种：`maps`包中的数据** [**maps** package](http://cran.rstudio.com/package=maps): - the data frame from returned from `map()` ```{r warning=FALSE} # 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) ``` ## 地图选择 ### 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](https://github.com/leaflet-extras/leaflet-providers)来改变，更全面的例子见[这里](http://leaflet-extras.github.io/leaflet-providers/preview/index.html)。 ```{r fig.height=4} m % setView(lng=116.67498, lat=40.40652, zoom = 12) m %>% addTiles() m %>% addProviderTiles(providers$Stamen.Toner) m %>% addProviderTiles(providers$CartoDB.Positron) m %>% addProviderTiles(providers$Esri.NatGeoWorldMap) ``` ### WMS Tiles 可以利用`addWMSTiles()`来添加WMS (Web Map Service) tiles。 The map below shows the Base Reflectivity (a measure of the intensity of precipitation occurring) using the WMS from the [Iowa Environmental Mesonet ](http://mesonet.agron.iastate.edu): ```{r fig.height=4} leaflet() %>% addTiles() %>% setView(-93.65, 42.0285, zoom = 4) %>% addWMSTiles( "http://mesonet.agron.iastate.edu/cgi-bin/wms/nexrad/n0r.cgi", layers = "nexrad-n0r-900913", options = WMSTileOptions(format = "image/png", transparent = TRUE), attribution = "Weather data © 2012 IEM Nexrad" ) ``` ### 多种底图叠加 还可以通过设置透明色的方式，将多种底图进行叠加显示 ```{r fig.height=4} m %>% addProviderTiles(providers$MtbMap) %>% addProviderTiles(providers$Stamen.TonerLines, options = providerTileOptions(opacity = 0.35)) %>% addProviderTiles(providers$Stamen.TonerLabels) ```