您可以只使用从中检索的多边形maps
。当然可以使用任何其他合适的来源,就像@JanLauGe提到的那样。
获得特定国家的多边形后,您可以将它们转换为SpatialPolygonsDataFrame
. 如果您只想显示感兴趣的区域,您也可以创建一个蒙版。
自然,之后您可以使用标准 Leaflet 方法轻松添加任何点或标记,例如addCircleMarkers( lng, lat )
.
library(ggmap)
library(leaflet)
library(magrittr)
library(maps)
library(maptools)
library(raster)
library(rgeos)
library(sp)
country <- 'italy';
zoomLevel <- 6;
# Get the map ( class is map )
ita.map <- map( country, fill = TRUE, col = 1, plot = F );
# Get the geo center for lazyness
ita.center <- geocode( "italy" );
# Extract the names from ita.map.
# e.g. "Trapani:I. Le Egadi:I. Marettimo" -> "Trapani"
# note: any other solution is fine, because we don't really need them, but they
# can be useful later
ita.map.ids <- sapply( strsplit( ita.map$names, ':' ), function(x) x[1] );
# Convert our map object to SpatialPolygons
ita.sp <- map2SpatialPolygons( ita.map, IDs=ita.map.ids,
proj4string=CRS("+proj=longlat +datum=WGS84"))
# Note: if you only need a unified polygon, it can be achieved by fortify
# ita.sp.df <- fortify( ita.sp );
# Finally convert our SpatialPolygons to SpatialPolygonsDataFrame
tmp.id.df <- data.frame( ID = names(ita.sp) );
rownames( tmp.id.df ) <- names( ita.sp );
ita.spdf <- SpatialPolygonsDataFrame( ita.sp, tmp.id.df );
# Visualize
l.ita.map <- leaflet( ita.spdf ) %>%
setView(lng = ita.center$lon, lat = ita.center$lat, zoom = zoomLevel ) %>%
addTiles() %>%
addPolygons( data = ita.spdf, weight = 1, fillColor = "blue", fillOpacity = 0.5 );
l.ita.map

####### Alternatively if a mask if needed #######
# Get a plane of the world
wld.sp <- rasterToPolygons( raster(ncol = 1, nrow = 1, crs = proj4string(ita.sp) ) );
# Cut our country polygon from the plane to get our target mask
ita.sp.mask <- gDifference( wld.sp, ita.sp );
# Convert our ita.sp.mask (SpatialPolygons) to SpatialPolygonsDataFrame
tmp.id.df <- data.frame( ID = "1" );
rownames( tmp.id.df ) <- names( ita.sp.mask );
ita.mask.spdf <- SpatialPolygonsDataFrame( ita.sp.mask, tmp.id.df );
# Coordinates of Rome
ita.rome.center <- geocode( "Rome, italy" );
# Visualize
l.ita.mask.map <- leaflet( ita.mask.spdf ) %>%
setView( lng = ita.center$lon, lat = ita.center$lat, zoom = zoomLevel ) %>%
addTiles() %>%
addPolygons( data = ita.mask.spdf, fillColor = "white", fillOpacity = 1.0, color = "black", weight = 1 ) %>%
addCircleMarkers(lng = ita.rome.center$lon, lat = ita.rome.center$lat );
l.ita.mask.map;

感谢@fdetsch的建议!