Map R language

leaflet package

LeafletR Mainly used R The grammar of the language encapsulates JS Version of Leaflet, Can be in R Linguistic plot window , utilize html5 Technology displays various maps , You can also draw your own element graphics .

It has the following functions ：
Interactive map browsing （ The zoom 、 translation ）
Use a variety of underlays for any combination
Load map tiles （WMTS）
Point feature locator
Polygon feature markers
Line feature tags
Pop-up window
Parse load GeoJson
from R perhaps RSutido Create a map window
You can embed the map knitr/R Package generated Markdown In the document , Or is it Shiny To make the APP in .
It can be obtained directly through SP Bao Shengcheng （ load ） Spatial objects and data frames containing longitude and latitude are displayed .
You can set the map range and encapsulate custom mouse events .

Generally speaking , Its basic use steps are as follows ：

1、 load leaflet package
2、 adopt leaflet Package create map control .
3、 Through the method of layer operation （ Such as addTiles、 addMarkers、 addPolygons） To process layer data , And modify various parameters of the map plug-in , To display the layer on the map control .
4、 You can repeat step 3 , You can add more layer data .
5、 Display the map components . Complete the drawing .

Here's an example ：

m <- leaflet()
at <- addTiles(m)
addMarkers(at,lng=116.391, lat=39.912, popup=" This is Beijing ")

leaflet()%>%addTiles()%>%addMarkers(lng=116.391, lat=39.912, popup=" This is Beijing ")

In the official documents , For this kind of writing that requires repeated container nesting , Pipeline operators are provided “%>%” To achieve , Its main function is to put the previous sentence （ Variable ） Pass to the next statement , And as the first parameter , The three sentences above , Use the pipe operator to write , as follows , The output result is exactly the same , But the sentence becomes simple .

Two 、 Map control

stay leaflet When the package is initialized , The general call leaflet() This method , This method is to initialize the map control , A map container will be generated , All layer operations in the future , All in this container . Generally speaking , This method is used as the first parameter of other methods . We can set parameters by display or by pipeline operators %>% To pass this container to other methods .

The basic methods of map control include the following three ：

setView() : Set the display level and zoom scale of the map 、 And the center of the map .
fitBounds()： Set the scope of the map , It is usually a rectangle , Structure is ：[lng1, lat1] – [lng2, lat2].
clearBounds()： Clear the range setting of the map .

Here's an example ：

m<- leaflet()
m<- setView(m,lng=116.38,lat=39.9,zoom=9)
addTiles(m)

Or use the pipe operator

leaflet()%>%setView(lng=116.38,lat=39.9,zoom=9)%>%addTiles()

Initialization is changed to 3 Class words , give the result as follows ：

leaflet()%>%setView(lng=116.38,lat=39.9,zoom=3)%>%addTiles()

leaflet Packages support various objects related to spatial information , Including the use of sp Space object defined by package , and R Data frame with spatial information in language , As shown below ：
And R dependent ：

The matrix is composed of longitude and latitude information
Data frame with latitude and longitude fields .

And sp Package related ：

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

And that is maps Various spatial graphic information in the bag

These objects can be used directly leaflet The method inside , Add to the map as a layer . So let's go through leaflet To draw some maps

Of course , The simplest , Or draw points , Through latitude and longitude , Draw the dots , Our husband orders randomly in a batch ：

df = data.frame(Lat = rnorm(100), Lon = rnorm(100))

Then draw it ：

m <-leaflet(df)
addCircles(m)

# How to write it 2：

df %>%leaflet()%>%addCircles()

leaflet Compared with other map packages , There are many advantages and disadvantages ,

First , Drawing a map is simple and fast , Because they are all based on suppliers tiles, A line of code can render Basic widget Map .

Support pipeline parameter transfer , Add layer by layer , The code structure is clearer .

secondly , There's a lot of tiles Suppliers can choose , Including Gaud 、google、Stamen, Esri, OpenWeatherMap,NASA,

Wait for dozens tiles supplier . Of course, some of them need to be registered . Among them google You can bypass registration , It's very rare .

For adding markers Icon ,shapes shape , Lines, etc , Extremely convenient , This is in ggplot2 It is difficult to do .

Support grid data ,rasters Raster data is a map based on pixels . It can be seen that ,leaflet It is highly inclusive .

Support multiple projection coordinate systems , You can even customize the coordinate system , This is very important in some special scenes .

Of course, there is more important , It has certain interaction ability , You can zoom and drag ,

Simple layer switching does not need to be used Shiny. Make it easier to get started .

Other features , First tiles It is based on suppliers , It has to be networked ,

Secondly, the color support is different , Only support HEX Sum of color Spaces colors() Color names in . Of course, there are several built-in palette function , Very special .

1.Widget Set up

Widget Map box settings , To be sure Widget The basic parameters of ,

Include CRS Coordinate system ,widget The central coordinates of ,zoom level( The zoom ) The scope of the , widget Boundary coordinates ,data Data etc. .

1.1

leafletOptions()

leaflet() There was a options Parameters , use leafletOptions() Function to specify , Can be controlled widget Zoom range .

grammar ：
1leafletOptions(minZoom = NULL, maxZoom = NULL, crs = leafletCRS(),
2 worldCopyJump = NULL, preferCanvas = NULL, …)

The key parameters ：
minZoom, Represents the minimum reduction factor , Apply to all map layers .
maxZoom, Represents the maximum magnification , Apply to all map layers .
crs, Indicates the specified coordinate system ,
preferCanvas, To indicate whether or not to leaflet.js The path appears on the map .
1library(leaflet)
2
3leaflet(options= leafletOptions(minZoom=0, maxZoom =18))

1.2

center 、 The zoom 、 The border

The key function ：
setView() , Set the map view( Include center Location and zoom level)
flyTo() , Switch to a specified location or zoom-level, Use smooth pan-zoom
fitBounds() , Set the boundary of the rectangular area of the map .view Limit to [lng1, lat1] - [lng2, lat2]
flyToBounds() , Switch to a specified rectangular area boundary of the map , Use smooth pan/zoom
setMaxBounds() , Limit the maximum boundary of the rectangular area of the map
clearBounds() , Clear the border of the rectangular area of the map , then view It will only be limited by the longitude and latitude data of the map layer .
grammar ：
setView(map, lng, lat, zoom, options = list())
flyTo(map, lng, lat, zoom, options = list())
fitBounds(map, lng1, lat1, lng2, lat2, options = list())
flyToBounds(map, lng1, lat1, lng2, lat2, options = list())
setMaxBounds(map, lng1, lat1, lng2, lat2)
ClearBounds (map)

Parameter interpretation ：
map, Express leaflet() Created map widget
lng, Express map center Longitude of , East longitude is positive
lat, Express map center Latitude of , North latitude is positive
zoom, Express zoom level
options, List reference , Pass on zoom or pan Parameters .
lngl, latl, lng2, lat2, Express widget The coordinates of the boundary .

1library(leaflet)
2
3#  Set the center coordinates and zoom level
4m <- leaflet() %>% addTiles() %>% setView(-71.0382679,42.3489054, zoom =18)56
#  Show the first view
7m %>% fitBounds(-72,40,-70,43) 
#  Set up view The border 89#  Show the second view
10m %>% clearBounds() #  Clear boundary restrictions , leaflet() Default to world map 

Data data

there Data It's not just drawing the data of administrative areas on the map , And include the data to be presented on the map .

Most layer adding functions have data Parameters , Usually use %>% Pipe symbols are gradually passed data Parameters .

leaflet() The following forms of data are usually supported .

Matrix data ( It consists of longitude and latitude ).

Data frame ( It consists of longitude and latitude ).

from sp Data transmitted by the package , Include ：

SpatialPoints( Data frame type )

Line()/Lines()

SpatialLines()( Data frame type )

Polygon()/Polygons()

SpatialPolygons()( Data frame type )

from maps Data transmitted by the package , Mainly map() Data frame passed by function .

For longitude and latitude, form matrix or data frame type data , On the move data When adding layers , Guess and match according to the variable name ：

If the variable name is lat, or latitude etc. , Then guess the latitude , When guessing , Case insensitive .

If the variable name is lng, long or longitude etc. , Then guess longitude , When guessing , Case insensitive .

You can also manually specify longitude and latitude variables , Use ~ grammar .

During parameter passing , Default the following data Parameters override the previous data Parameters .

1.3.1 data Designation of mid latitude and longitude / guess / Cover

1library(leaflet)23#  Auto guess match 

4set.seed(123)5df <- data.frame(Lat = 1:10, Long = rnorm(10))6leaflet(df)%>%addCircles()78#  Manually specify longitude and latitude variables , Results the same  leaflet(df) %>% addCircles(lng = ~Long,

9# lat = ~Lat)

1011#  stay add_xxx() Re specify parameters in the function to override , Results the same  leaflet() %>%

12# addCircles(data = df) leaflet() %>% addCircles(data = df, lat = ~Lat, lng

13# = ~Long)

1.3.2 sp Object's data

1library(leaflet)
2library(sp)
3library(RColorBrewer)
4
5Sr1 <- Polygon(cbind(c(2,4,4,1,2), c(2,3,5,4,2))) 
#4 For non repeating point coordinates , end to end 
6Sr2 <- Polygon(cbind(c(5,4,2,5), c(2,3,2,2))) 
#3 For non repeating point coordinates , Draw a triangle 
7Sr3 <- Polygon(cbind(c(4,4,5,10,4), c(5,3,2,5,5))) 
#4 For non repeating point coordinates , Draw a quadrilateral 
8Sr4 <- Polygon(cbind(c(5,6,6,5,5), c(4,4,3,3,4)), hole = TRUE) # hole = TRUE, It means hollow 
9
10
11Srs1 <- Polygons(list(Sr1),"s1") #'s1' Appoint ID Parameters , Only multiple polygons ID Parameters ,Polygon() No, ID Parameters 
12Srs2 <- Polygons(list(Sr2),"s2")
13Srs3 <- Polygons(list(Sr4, Sr3),"s3/4") #  Merge Sr3 and Sr4 polygon 
14
15#  List reference , Pass multiple polygon parameters 
16SpP <- SpatialPolygons(list(Srs1, Srs2, Srs3),1:3)
17
18leaflet(height ="300px") %>% addPolygons(data = SpP, fillColor = brewer.pal(3,19name ="Set1"))

1.3.3 from maps In the package for data

1library(leaflet)
2library(maps)
3library(RColorBrewer)
4
5mapStates <- map("state", fill = TRUE, plot = FALSE)
6leaflet(data= mapStates) %>% addTiles() %>% addPolygons(fillColor = brewer.pal(10,7 name="Paired"), stroke = FALSE)

1.3.4 Other parameters

Other drawing parameters support R The type of data that comes with it , Such as ： vector , Color vector , Data frame , It also supports ~ Appoint .

1library(leaflet)
2
3#  Make up a random data 
4m <- leaflet() %>% addTiles()
5df <- data.frame(lat = rnorm(100), lng = rnorm(100),size= runif(100,5,20),
6color= sample(colors(),100))
7
8m <- leaflet(df) %>% addTiles()
9#circle The radius of the icon does not change zoom change :
10m %>% addCircleMarkers(radius = ~size,color= ~color, fill = FALSE)
11#circle The radius of the icon does not change zoom change :
12m %>% addCircleMarkers(radius = runif(100,4,10),color= c("red"))

2.Basemaps Base map

leaflet Support Tilemap Base map of type ,

leaflet Support a variety of free third parties providers Of tiles, Include Stamen, Esri, OpenWeatherMap etc. ,

use names(providers) You can see all of providers.

2.1

Default Tiles(OpenStreetMap)

Use addTiles() Function add tiles And use the default parameters , The default is OpenStreetMap, Block Tiles.

1library(leaflet)
2
3m <- leaflet()%>%setView(lng = -71.0589, lat = 42.3601, zoom = 12)4m%>%addTiles()#  Show the street map 

The third party Tiles

call addProviderTiles() function , In the parameter providers$ Back plus tiles Just the name of the supplier . We need to pay attention to ： Some third parties tiles Need to register .

adopt options Parameter call providerTileOptions() Function can avoid some tiles Registration of .

If there is customized tiles Template URL link , Can be in addTiles() Call in function .

1library(leaflet)
2
3m <- leaflet()%>%setView(lng = -71.0589, lat = 42.3601, zoom = 12)
4
5#  Use Stamen.Toner  Of  tiles
6m%>%addProviderTiles(providers$Stamen.Toner)

Clever data conversion

By calling functions addWMSTiles() You can add WMS(Web Map Service) Of tiles.

Web Map service （WMS） It's a standard protocol , Describe how to pass through Internet Provide any geographical registration map image ,

This is usually generated by a map server using data from a GIS database .

The protocol standard consists of Open Geospatial Consortium（OGC） Development ,

And in 1999 First released in 2004 .WMS Provides a way to use HTTP A simple method of requesting geographical registration map image by interface .

WMS supplier （https://en.wikipedia.org/wiki/Web_Map_Service）

1library(leaflet)
2
3leaflet() %>% addTiles() %>% setView(-93.65,42.0285, zoom =4) %>% #  Stack one WMS Of tiles Layers 4addWMSTiles("http://mesonet.agron.iastate.edu/cgi-bin/wms/nexrad/n0r.cgi", layers ="nexrad-n0r-900913",
5 options = WMSTileOptions(format ="image/png", transparent = TRUE), attribution ="Weather data <U+00A9> 2012 IEM Nexrad")

Tiles Layer overlay

Multiple Tiles Layers can also be superimposed , But this situation is usually only used for the surface tiles Is translucent ,

Or in the options Manually specify the opacity in the parameter opacity.

opacity from 0( Completely transparent ) To 1( Completely opaque ).

1library(leaflet)
2
3m <- leaflet() %>% setView(lng = -71.0589, lat =42.3601, zoom =12)
4
5m %>% addProviderTiles(providers$MtbMap) %>% #  Bottom tiles
6 addProviderTiles(providers$Stamen.TonerLines, #  Stack one layer tiles, Show roads and streets 
7 options = providerTileOptions(opacity =0.35)) %>% # opacity Set opacity 
8 addProviderTiles(providers$Stamen.TonerLabels) #  superposition tiles, Display the road name , Street name , Airport icon .
 link ：https://blog.csdn.net/R3eE9y2OeFcU40/article/details/88324895