R语言绘制阿拉巴马郡选举分级地图报错求助

报错根源 #

Error: Discrete value supplied to continuous scale 是因为你试图将离散分类变量（比如标记Jones/Moore获胜的标签）传入需要连续数值的颜色刻度函数，两者类型不匹配导致冲突。

核心解决思路 #

要实现你要的10级RdBl配色（Jones胜区从浅到深蓝，Moore胜区从浅到深红），必须用连续的得票差值变量（而非离散胜负标签）来映射颜色梯度。

具体修正步骤 #

1. 预处理数据：计算得票差值 #

先给每个郡计算Jones与Moore的得票率差值，这个连续变量是颜色映射的核心：

# 假设你的选举数据框名为election_data
library(dplyr)
election_data <- election_data %>%
  mutate(margin = jones_pct - moore_pct)

2. 修正绘图代码 #

结合map_data和ggplot2，用scale_fill_gradientn自定义10级配色：

library(ggplot2)
library(maps)

# 获取阿拉巴马郡地图数据，统一列名方便合并
alabama_map <- map_data("county", region = "alabama") %>%
  rename(county = subregion)

# 合并地图数据与选举数据（务必保证county列的拼写、大小写完全一致）
map_election <- left_join(alabama_map, election_data, by = "county")

# 绘制分级统计图
ggplot(map_election, aes(x = long, y = lat, group = group, fill = margin)) +
  geom_polygon(color = "white", linewidth = 0.2) +
  coord_map() +
  # 自定义10级RdBl配色：从深红（Moore大胜）到浅红、中性白、浅蓝再到深蓝（Jones大胜）
  scale_fill_gradientn(
    colors = c("#8B0000", "#CD5C5C", "#FFA07A", "#FFE4E1", "#F5F5F5",
               "#E6F3FF", "#B0E0E6", "#4682B4", "#1E90FF", "#00008B"),
    breaks = seq(-50, 50, 10), # 根据你的实际得票差值范围调整
    labels = c("Moore +50%", "Moore +40%", "Moore +30%", "Moore +20%", "Moore +10%",
               "Jones +10%", "Jones +20%", "Jones +30%", "Jones +40%", "Jones +50%"),
    name = "Vote Margin"
  ) +
  theme_void() +
  labs(title = "Alabama Special Election Results by County")

3. 可选：离散分箱实现10级配色 #

如果希望将得票差值分成10个离散区间，可先用cut()分箱，再用离散配色：

# 分箱处理
election_data <- election_data %>%
  mutate(margin_bin = cut(margin, breaks = 10, labels = paste0("Tier ", 1:10)))

# 绘图
ggplot(map_election, aes(x = long, y = lat, group = group, fill = margin_bin)) +
  geom_polygon(color = "white", linewidth = 0.2) +
  coord_map() +
  scale_fill_manual(
    values = c("#8B0000", "#CD5C5C", "#FFA07A", "#FFE4E1", "#F5F5F5",
               "#E6F3FF", "#B0E0E6", "#4682B4", "#1E90FF", "#00008B"),
    name = "Vote Margin Tier"
  ) +
  theme_void()

关键注意事项 #

• 确保alabama_map和election_data的county列完全匹配（比如都是小写、无额外后缀），否则数据合并会失败
• 若你的得票差值范围不是-50到50，需调整breaks和labels的数值以匹配实际数据

内容的提问来源于stack exchange，提问作者data_life