我试图map2SpatialPolygons在显示美国国家子集的地图中创建核密度图.我一直收到一条错误,说"地图和身份证的长度不同".
我知道这段代码有效(来自map2SpatialPolygons的帮助):
nor_coast_poly <- map("world", "norway", fill=TRUE, col="transparent", plot=FALSE, ylim=c(58,72))
IDs <- sapply(strsplit(nor_coast_poly$names, ":"), function(x) x[1])
nor_coast_poly_sp <- map2SpatialPolygons(nor_coast_poly, IDs=IDs, proj4string=CRS("+proj=longlat +datum=wgs84"))
此代码也有效(映射整个美国时):
usmap <- map('usa', fill=TRUE, col="transparent", resolution=0, plot=FALSE)
uspoly <- map2SpatialPolygons(usmap, IDs=usmap$names, proj4string=CRS("+proj=longlat +datum=WGS84"))
但是这段代码没有:
states.to.plot=c("illinois", "indiana", "ohio")
dmap<-map("state", regions=states.to.plot, col="transparent", plot=FALSE)
dpoly <- map2SpatialPolygons(dmap, IDs=dmap$names, proj4string=CRS("+proj=longlat +datum=WGS84"))
它抛出错误:
Error in map2SpatialPolygons(dmap, IDs = dmap$names, proj4string = CRS("+proj=longlat +datum=WGS84")) :
map and IDs differ in length
使用map("状态"...)时如何正确识别ID？