如何根据R tmap中的属性值更改多边形的边框颜色

Question

我正在尝试使用 R 的 tmap 包创建一个地图，该包对于属性的每个值都有不同的颜色轮廓。例如，在填充多边形时，我可以简单地执行 tm_polygons(col = "variable") 来获取基于“variable”属性填充多边形的地图。我想做类似的事情，但只有边框，而不是填充。我没有找到任何好的答案，所以我希望在这里得到一些帮助！

下面是一个说明这一想法的示例：

library(tigris)
library(tmap)
library(tidyverse)

region_2 = states() %>% filter(REGION == 2)
states_of_interest = region_2 %>% filter(NAME %in% c("Ohio", "Missouri", "Wisconsin"))

tm_shape(region_2) + tm_polygons(col = "white") + tm_shape(states_of_interest) + .......

我不太确定如何继续

基本上，我希望俄亥俄州、密苏里州和威斯康星州的边界具有不同的颜色，以使用 感兴趣的州。任何帮助将不胜感激！

Answer 1

一个可能的解决方法是将您的 POLYGONS 转换为 LINESTRING 并继续使用 tm_lines()：

library(tigris)
#> To enable caching of data, set `options(tigris_use_cache = TRUE)`
#> in your R script or .Rprofile.
library(tmap)
library(tidyverse)

region_2 = states() %>% filter(REGION == 2)
#> Retrieving data for the year 2020
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states_of_interest = region_2 %>%
  filter(NAME %in% c("Ohio", "Missouri", "Wisconsin"))

states_lines <- states_of_interest %>% sf::st_cast("MULTILINESTRING")


tm_shape(region_2) + 
  tm_polygons(col = "white") +
  tm_shape(states_lines) +
  tm_lines(col="NAME", lwd=2)

^{由 reprex 包 (v2.0.1)}