如何将州名称转换为纬度和经度以在 R 中使用 ggvis 创建等值线？

Question

我想用 ggvis 包为每个州的收入值创建一个等值线。下面是我的数据。我认为映射数据需要纬度和经度列。任何人都知道如何将州名称转换为纬度和经度？非常感谢！

mapdata<-data.frame(
 state=c("alabama","alaska","arizona","arkansas","california","colorado","connecticut","delaware","florida","georgia","hawaii","idaho","illinois","indiana","iowa","kansas","kentucky","louisiana","maine","maryland","massachusetts","michigan", "minnesota","mississippi","missouri","montana","nebraska","nevada","new hampshire","new jersey","new mexico","new york","north carolina","north dakota","ohio","oklahoma", "oregon","pennsylvania","rhode island","south carolina","south dakota","tennessee","texas","utah","vermont","virginia","washington","west virginia","wisconsin","wyoming"),
  income=runif(50,min=100,max=9000))

Answer 1

这是一种方法。我使用的是 ggplot 而不是 ggVis 但这应该可以帮助您入门。

library(raster)       # for getData(...)
library(ggplot2)
library(data.table)
usa   <- getData('GADM',country='USA',level=1)         # shapefile of US states
shp   <- usa[(!usa$NAME_1 %in% c("Alaska","Hawaii")),] # remove AK, HI for this example
gg.dt <- setDT(fortify(shp))               # convert shapefile to format ggplot can use
# merge with attribute table
gg.dt <- gg.dt[setDT(cbind(id=rownames(shp@data),shp@data)),on="id"]  
gg.dt[,state:=tolower(NAME_1)]             # convert state names to lower case                                     
gg.dt <- gg.dt[setDT(mapdata),on="state"]  # merge with mapdata

ggplot(gg.dt, aes(x=long, y=lat, group=group,fill=revenue)) + 
  geom_polygon(color="grey50", size=0.1)+
  scale_fill_gradientn(colours=rev(heat.colors(10)))+
  coord_map()

所以这里有一个 ggvis 解决方案（可能应该是一个单独的答案，但 WTH）。事实证明，上面的 shapefile 分辨率非常高，ggvis 无法处理那么大的文件。所以我们在这里下载一个美国州界的低分辨率 shapefile，使用 data.frames 合并（使用低分辨率 shapefile 足够快），然后使用 ggvis.

渲染

library(rgdal)   # for readOGR(...)
library(ggplot2) # for fortify(...)
library(ggvis)
# load low resolution US state shapefile (1:20MM)
url   <- "http://www2.census.gov/geo/tiger/GENZ2014/shp/cb_2014_us_state_20m.zip"
tf    <- tempfile()
td    <- tempdir()
download.file(url,tf, mode="wb")   # download shapefile archive of US state boundaries
unzip(tf, exdir=td)                # unzip into directory td

usa <- readOGR(dsn=td, layer="cb_2014_us_state_20m")
shp <- usa[(!usa$STUSPS %in% c("AK","HI")),] # remove AK, HI for this example

gg.df       <- fortify(shp)                     # convert shapefile to format ggvis can use
gg.df       <- merge(gg.df,cbind(id=rownames(shp@data),shp@data),by="id")   # merge with attribute table
gg.df$state <- tolower(gg.df$NAME)              # convert state names to lower case                                     
gg.df       <- merge(gg.df,mapdata,by="state")  # merge with mapdata
gg.df       <- gg.df[order(gg.df$order),]       # reset to original order

gg.df %>%
  group_by(group) %>%
  ggvis(~long, ~lat)  %>%
  layer_paths(fill= ~revenue)

有一篇关于使用 ggvis here 创建等值线图的不错的博客 post。如果您想要自定义颜色（如之前的回答），请参阅 post。

如何将州名称转换为纬度和经度以在 R 中使用 ggvis 创建等值线？

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