修正Leaflet图例：将彩色方块改为对应样式线条

你的问题出在默认的addLegend生成的是填充方块，但你的图层都是无填充的多边形边框（fill=FALSE），需要让图例显示匹配的线条样式（颜色、线宽、虚线）。

修改你的addLegend代码，指定符号类型为线条，并配置对应图层的样式参数：

# 替换原有的addLegend部分
addLegend(position = "bottomright", 
          colors = c("#000000", "#0000FF", "#FF0000"), 
          labels = c("Blocks 2000", "Tracts 2000", "Tracts 2010"), 
          title = "Legend",
          symbol = "line",       # 将图例符号设为线条
          weight = c(0.5, 3, 3), # 对应三个图层的线宽
          dashArray = c("2", "", "5,5"), # 对应三个图层的虚线样式，空字符串为实线
          fill = FALSE           # 禁用填充，只显示线条
)

关键参数说明： #

• symbol = "line"：告诉Leaflet生成线条样式的图例项，而非默认的填充方块
• weight：按顺序匹配三个图层的线宽（Blocks 2000为0.5，两个Tracts图层为3）
• dashArray：按顺序匹配虚线规则（Blocks 2000为"2"，Tracts 2000为空字符串即实线，Tracts 2010为"5,5"）
• fill = FALSE：确保图例项没有填充色，只显示边框线条

修改后的完整地图代码如下：

az_2000 <- tracts(state = "Arizona", year = 2000) %>% 
  select(c(CTIDFP00)) %>% rename("geoid" = "CTIDFP00")
az_2000 <- st_transform(az_2000, 4326)

az_bg2000 <- blocks(state = "Arizona", year = 2000) %>% 
  select(c(BLKIDFP00)) %>% rename("geoid" = "BLKIDFP00")
az_bg2000 <- st_transform(az_bg2000, 4326) # 显式指定CRS，和其他图层保持一致

az_2010 <- tracts(state = "Arizona", year = 2010) %>% 
  select(c(GEOID10)) %>% rename("geoid" = "GEOID10")
az_2010 <- st_transform(az_2010, 4326)
    

# Create a map with the three layers
map <- leaflet() %>%
  addTiles() %>%
  addPolygons(data = az_bg2000,
              fill = FALSE,
              color = "#000000",
              dashArray = "2",
              weight = 0.5,
              label = "Blocks 2000") %>%
  addPolygons(data = az_2000, 
              fill = FALSE, 
              color = "#0000FF", 
              weight = 3,
              label = "Tracts 2000") %>%
  addPolygons(data = az_2010, 
              fill = FALSE, 
              color = "#FF0000",
              dashArray = "5,5",
              weight = 3,
              label = "Tracts 2010") %>%
  addLegend(position = "bottomright", 
            colors = c("#000000", "#0000FF", "#FF0000"), 
            labels = c("Blocks 2000", "Tracts 2000", "Tracts 2010"), 
            title = "Legend",
            symbol = "line",
            weight = c(0.5, 3, 3),
            dashArray = c("2", "", "5,5"),
            fill = FALSE)

另外注意：原代码中az_bg2000的st_transform未指定CRS，建议显式设置为4326，避免潜在的坐标系不匹配问题。

内容的提问来源于stack exchange，提问作者tchoup