如何在R的usmap包中叠加州边界与县热力地图？

我需要在县级热力地图上清晰显示州边界，但现有代码的州边界不够突出，尝试了两段代码都没解决问题。

原始代码片段1 #

# 获取所有州的多边形数据
states_sf <- get_urbn_map(map = "states", sf = TRUE)

# 筛选指定州的多边形数据
selected_states <- c("AL", "AR", "CT", "DC", "DE", "FL", "GA", "LA", 
                     "MA", "MD", "ME", "MS", "NC", "NH", "NJ", "NY", 
                     "PA", "RI", "SC", "TX", "VA", "VT", "WV")
selected_states_sf <- states_sf[states_sf$ST %in% selected_states, ]

# 假设Hurricane$total_wind是数值型变量
plot_usmap("counties", data = Hurricane, values = "total_wind",
           include = selected_states,
           color = "black"
) +
  ggplot2::scale_fill_continuous(low = "snow2", high = "red", guide = FALSE) +
  geom_sf(data = selected_states_sf, fill = NA, color = "black", size = 0.5) +  # 调整州边界线宽
  theme_minimal() +
  
  # 移除网格线
  coord_sf(datum = NA, crs = st_crs(states_sf)) +   # 显式设置坐标系
  labs(fill = "Random Data") + 
  scale_fill_gradient2(low='snow2', high='red') + 
  theme_bw() + 
  theme(
    # 隐藏面板边框和网格线
    panel.border = element_blank()
  )

原始代码片段2 #

plot_usmap("counties", data = Hurricane, values = "total_wind",
           include = c("AL", "AR", "CT", "DC", "DE", "FL", "GA", "LA", 
                       "MA", "MD", "ME", "MS", "NC", "NH", "NJ", "NY", 
                       "PA", "RI", "SC", "TX", "VA", "VT", "WV")
) +
  ggplot2::scale_fill_continuous(low = "ghostwhite", high = "red", guide = FALSE)

问题分析 #

• 片段1的问题：
  1. 重复调用填充比例尺（scale_fill_continuous和scale_fill_gradient2），后者会覆盖前者，造成冗余。
  2. geom_sf叠加的州边界因坐标系不匹配（plot_usmap默认Albers投影，与get_urbn_map的CRS不一致）导致显示异常，且size=0.5的线宽仍不够突出。
  3. 同时使用theme_minimal()和theme_bw()，主题设置冲突，干扰边界显示。
• 片段2的问题：完全没有添加州边界绘制逻辑，自然看不到州边界。

解决方案 #

方案1：直接用plot_usmap内置参数设置州边界

plot_usmap支持直接绘制州边界，无需额外导入sf数据，坐标系自动匹配，操作更简洁：

selected_states <- c("AL", "AR", "CT", "DC", "DE", "FL", "GA", "LA", 
                     "MA", "MD", "ME", "MS", "NC", "NH", "NJ", "NY", 
                     "PA", "RI", "SC", "TX", "VA", "VT", "WV")

# 先绘制县级热力图，再叠加州边界（确保州边界在最上层）
plot_usmap(regions = "counties", data = Hurricane, values = "total_wind",
           include = selected_states,
           fill = "total_wind",
           color = "gray80"  # 县级边界设为浅灰色，避免和州边界冲突
) +
  # 叠加州边界，设置粗线宽和高对比色
  plot_usmap(regions = "states", include = selected_states,
             fill = NA, color = "black", size = 1.2) +
  scale_fill_gradient2(low = "snow2", high = "red", guide = FALSE) +
  labs(fill = "总风速") +
  theme_bw() +
  theme(
    panel.border = element_blank(),
    axis.text = element_blank(),
    axis.title = element_blank()
  )

方案2：修复sf数据叠加的问题

如果坚持用sf数据叠加，需统一坐标系并调整绘制参数：

library(usmap)
library(sf)
library(ggplot2)

# 获取州数据并转换为usmap默认的Albers投影
states_sf <- get_urbn_map(map = "states", sf = TRUE) %>%
  st_transform(crs = usmap_crs())

selected_states <- c("AL", "AR", "CT", "DC", "DE", "FL", "GA", "LA", 
                     "MA", "MD", "ME", "MS", "NC", "NH", "NJ", "NY", 
                     "PA", "RI", "SC", "TX", "VA", "VT", "WV")
selected_states_sf <- states_sf[states_sf$ST %in% selected_states, ]

plot_usmap("counties", data = Hurricane, values = "total_wind",
           include = selected_states,
           color = "gray80"
) +
  scale_fill_gradient2(low = "snow2", high = "red", guide = FALSE) +
  # 叠加州边界，设置粗线宽，关闭美学参数继承
  geom_sf(data = selected_states_sf, fill = NA, color = "black", size = 1.2, inherit.aes = FALSE) +
  theme_bw() +
  theme(
    panel.border = element_blank(),
    axis.text = element_blank(),
    axis.title = element_blank()
  )

关键调整点：

• 把县级边界设为浅灰色，与黑色州边界形成对比，突出州边界层级。
• 州边界线宽调整为1.2左右，确保视觉上足够显眼。
• 方案2中需统一坐标系，避免边界错位。

内容的提问来源于stack exchange，提问作者Anupam Ghosh