我是一个 R 菜鸟，甚至是关于 choropleths 和映射的菜鸟。
我已经看到了这个线程和线程链接到的其他线程，但就是无法解决这个问题。我正在尝试在等值线地图上绘制一些美国人口普查数据，尽管尝试了各种组合，但我什至不知道问题出在哪里。
这是简要代码：如果需要，可以提供更详细的代码。
code <- c(1:2, 4:6, 8:13, 15:42, 44:51, 53:56, 72)
statename <- c("Alabama", "Alaska", "Arizona", "Arkansas", "California", "Colorado", "Connecticut", "Delaware", "District of Columbia", "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", "Puerto Rico")
statelist <- data.frame(code, statename)
populDataNew <- merge(x = populData, y = statelist, by.x = "State", by.y = "code")
incomestate <- ddply(populData, c("Income", "statename"), summarise, incomebystate = sum(Income))
edu <- select(populDataNew, c(statename, EduAttainment), na.rm=TRUE)
edusum <- ddply(edu, c("statename"), summarise, edubystate = mean(EduAttainment))
states_map <-map_data("state")
states_map <- fortify(states_map, region = "statename")
m <- ggplot(edusum, aes(map_id = statename)) + geom_map(aes(fill = edubystate), map = states_map) + expand_limits(x = states_map$long, y = states_map$lat)
m
注意：尽管不明白为什么，我仍在使用 fortify :(
我得到的错误是：
Error in unit(x, default.units) : 'x' and 'units' must have length > 0