在 R 中的 ggmap 中的 geom_polygon 数据上绘制文本标签

Question

我正在尝试使用 ggmap 制作具有三层的地图。图层如下：

美国地图（碳粉精简版）
一组为状态着色的几何体（下面的模拟数据）
州名标签，作为每个州中心的注释。

为此，我创建了一张美国各州地图，其中各州按随机值 (rnorm) 着色，这部分成功了。从这里开始，我尝试使用 geom_text 在每个州中心的经度和纬度坐标处打印每个州的缩写。失败的部分是 'geom_text' 覆盖，错误如下：

Error: 'x' and 'units' must have length > 0 In addition: Warning messages: 1: In gpclibPermit() : support for gpclib will be withdrawn from maptools at the next major release 2: Removed 855070 rows containing missing values (geom_text).

这是我努力运行编写的脚本。它将下载 shapefile 和状态中心数据，以及模拟数据以填充状态。我已经对其进行了测试，它符合我注释掉的内容（geom_text 层）。

我已经搜索过这个问题的答案，所以如果您对如何做我正在尝试的事情有任何建议，请告诉我。如果有更好的策略将标签放置在多边形填充的顶部，我会洗耳恭听（在这种情况下是眼睛）。

###Combining Census data with a tract poly shapefile
library(maptools)
library(ggplot2)
library(gpclib)
library(ggmap)
library(rgdal)
library(dplyr)

#Set working directory to where you want your files to exist (or where they already exist)
setwd('~/Documents/GIS/USCensus/')
#Read and translate coord data for shape file of US States
if(!file.exists('tl_2014_us_state.shp')){
        download.file('ftp://ftp2.census.gov/geo/tiger/TIGER2014/STATE/tl_2014_us_state.zip',
                      'tl_2014_us_state.zip')
        files <- unzip('tl_2014_us_state.zip')
        tract <- readOGR(".","tl_2014_us_state") %>% spTransform(CRS("+proj=longlat +datum=WGS84"))
} else {
        tract <- readOGR(".","tl_2014_us_state") %>% spTransform(CRS("+proj=longlat +datum=WGS84"))
}

#two column dataset of state abbreviations and center of state
#Downloadable from: https://dev.maxmind.com/static/csv/codes/state_latlon.csv
if(!file.exists('state_latlon.csv')){
        download.file('http://dev.maxmind.com/static/csv/codes/state_latlon.csv','state_latlon.csv')
}
centers <- read.csv('state_latlon.csv')
#Change values of longitude and latitude from state center data so as not to interfere with shapefile at merge
names(centers)[2:3] <- c('long_c','lat_c')

#simulated data for plotting values
mydata<- data.frame(rnorm(55, 0, 1)) #55 "states" in the coord dataset for state centers
names(mydata)[1] <- 'value'

#hold names in tract dataset and for simulated data
ntract<-names(tract)
ndata<-names(mydata) 

#Turn geo data into R dataframe
gpclibPermit()
tract_geom<-fortify(tract,region="STUSPS")

#Merge state geo data with simulated data
state_data <- cbind(centers,mydata)
#merge state center and value data with shapefile data
tract_poly <- merge(state_data,tract_geom,by.x="state",by.y="id", all = F) 
tract_poly<-tract_poly[order(tract_poly$order),]

#Create map of US
mymap <- get_stamenmap(bbox = c(left = -124.848974,
                                bottom = 24.396308,
                                right = -66.885444,
                                top = 49.384358),zoom=5,
                       maptype="toner-lite")

#This plots a map of the US with just the state names as labels (and a few other landmarks). Used for reference
USMap <- ggmap(mymap,extent='device') +
        geom_polygon(aes(x = long, y = lat, group = group, fill = value),
                     data = tract_poly,
                     alpha = 1, 
                     color = "black",
                     size = 0.2) #+
#         geom_text(aes(x = long_c, y = lat_c, group = group, label = state),
#                   data= tract_poly,
#                   alpha = 1,
#                   color = "black")

USMap

Answer 1

试试这个

centroids <- setNames(do.call("rbind.data.frame", by(tract_poly, tract_poly$group, function(x) {Polygon(x[c('long', 'lat')])@labpt})), c('long', 'lat')) 
centroids$label <- tract_poly$state[match(rownames(centroids), tract_poly$group)]
USMap + with(centroids, annotate(geom="text", x = long, y=lat, label = label, size = 2.5))

()

Answer 2

对于最终的问题，这是一条奇怪的错误消息。沿途的某个地方，您已经翻转了中心的纬度和经度。（我也考虑了上面 elpi 的建议，并没有直接使用你的中心数据集重复绘制缩写）。下面的代码有效，但我建议修复您的中心数据集。

centers$new_long <- centers$lat_c
centers$new_lat <- centers$long_c
USMap <- ggmap(mymap,extent='device') +
        geom_polygon(aes(x = long, y = lat, group = group, fill = value),
                     data = tract_poly,
                     alpha = 1, 
                     color = "black",
                     size = 0.2) +
         geom_text(aes(x = new_long, y = new_lat, label = state),
                   data= centers,
                   alpha = 1,
                   color = "black")

在 R 中的 ggmap 中的 geom_polygon 数据上绘制文本标签

Plotting text labels over geom_polygon data in ggmap in R

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