在 ggplot 地图上难以结合 geom_path 和 geom_text

Question

我正在尝试使用 geom_path 和 geom_text 创建带标签的地图，但进展不顺利。我可以分别使用每个 geom_path 和 geom_text，但我似乎无法让它们一起工作。我认为它与 geom_polygon 有关，但我不确定是什么。

这是我为映射准备 shapefile 的方式：

meck.hiv <- as(meck.hiv, "Spatial")
meck.hiv@data$seq_id <- seq(1:nrow(meck.hiv@data)) #create unique id for each polygon
meck.hiv@data$id <- rownames(meck.hiv@data)
meck.hivdf <- fortify(meck.hiv) #fortify the data
zipcodedf <- merge(meck.hivdf, meck.hiv@data,
               by = "id")# merge the "fortified" data with the data from our spatial object
cnames <- aggregate(cbind(long, lat) ~ zip, data=zipcodedf, FUN=function(x)mean(range(x))) #get the names of our zipcode (and center the coordinates for labels)

有了这个，我可以得到以下地图：

有标签，没有路径：

p2 <- ggplot(data = zipcodedf, aes(x = long, y = lat)) +
  geom_polygon(aes(group=group, fill=hispanic.dis)) +
  geom_text(data=cnames, aes(long, lat, label = zip), size=3, fontface='bold', color="black")+ #This put in zip code names
  scale_fill_brewer(breaks=c(1, 2, 3, 4, 5, 6, 7), labels=c("<5", "5-10", "11-15", "16-20", "21-25", "26-30", "31+"), palette="Reds",
                    na.value="darkgrey") +  
  coord_equal() +
  theme(panel.background= element_rect(color="black")) +
  theme(axis.title = element_blank(), axis.text = element_blank()) +
  labs(title = "Hispanic Population by Zip Code", fill="Hispanic Population (% of Total)")

Resulting map with labels but no path

路径，但没有标签：

p3 <- ggplot(data = zipcodedf, aes(x = long, y = lat, group = group, fill = hispanic.dis)) +
  geom_polygon() +
  geom_path(color = "black", size = 0.2)+ #Oddly, use of geom_path with the above leads to weird stuff, but we can customize map lines without labels here
  scale_fill_brewer(breaks=c(1, 2, 3, 4, 5, 6, 7), labels=c("<5", "5-10", "11-15", "16-20", "21-25", "26-30", "31+"), palette="Reds",
                    na.value="darkgrey") + 
  coord_equal() +
  theme(panel.background=element_blank())+
  theme(panel.background= element_rect(color="black")) +
  theme(axis.title = element_blank(), axis.text = element_blank()) +
  labs(title = "Hispanic Population by Zip Code", fill="Hispanic Population(% of Total)")

Resulting path with paths but no labels

尝试合并

p4 <- ggplot(data = zipcodedf, aes(x = long, y = lat)) +
  geom_polygon(aes(group=group, fill=hispanic.dis)) +
  geom_text(data=cnames, aes(long, lat, label = zip), size=3, fontface='bold', color="black")+
  geom_path(color = "black", size = 0.2)+ #Oddly, use of geom_path with the above leads to weird stuff, but we can customize map lines without labels here
  scale_fill_brewer(breaks=c(1, 2, 3, 4, 5, 6, 7), labels=c("<5", "5-10", "11-15", "16-20", "21-25", "26-30", "31+"), palette="Reds",
                    na.value="darkgrey") + 
  coord_equal() +
  theme(panel.background=element_blank())+
  theme(panel.background= element_rect(color="black")) +
  theme(axis.title = element_blank(), axis.text = element_blank()) +
  labs(title = "Hispanic Population by Zip Code", fill="Hispanic Population(% of Total)")

Resulting screwed up plot with paths and labels

我的故障排除表明 geom_path 如何与 geom_polygon 和 ggplot() 进行交互，但是如果我将所有指令移到 geom_polygon 中，路径根本不会显示（尽管会生成一个图），如果我将所有指令移到 ggplot() 中，我会收到一个错误：“FUN 中的错误（X[[i]]，...）：找不到对象 'group'”（如下）。

p5 <- ggplot(data = zipcodedf, aes(x = long, y = lat, group = group, fill = hispanic.dis)) +
  geom_polygon() +
  geom_path(color = "black", size = 0.2)+ 
  geom_text(data=cnames, mapping=aes(x=long, y=lat))+#Oddly, use of geom_path with the above leads to weird stuff, but we can customize map lines without labels here
  scale_fill_brewer(breaks=c(1, 2, 3, 4, 5, 6, 7), labels=c("<5", "5-10", "11-15", "16-20", "21-25", "26-30", "31+"), palette="Reds",
                    na.value="darkgrey") + 
  coord_equal() +
  theme(panel.background=element_blank())+
  theme(panel.background= element_rect(color="black")) +
  theme(axis.title = element_blank(), axis.text = element_blank()) +
  labs(title = "Hispanic Population by Zip Code", fill="Hispanic Population(% of Total)")

感谢任何帮助。如果我需要提供更多信息，请告诉我。

Answer 1

{ggplot2} 的分层和继承有时会令人困惑。我希望以下内容有所帮助。还要检查你是否真的想要一个“额外的”geom_path() 层。感觉就像你想描绘/突出县界。另请注意，示例中使用color 为图层设置boundary(line) 颜色。

我必须模仿您的问题，因为您没有提供可重现的示例。初始代码是为我获取北卡罗来纳州的地图数据。我为县名构建了一个 cnames 数据框。您应该能够将此应用于县级的邮政编码问题... :)

library(dplyr)
library(ggplot)
library(maps)    # helper package to get some map data
library(mapdata) # helper for some map data

counties <- map_data("county") %>% filter(region == "north carolina")
head(counties)

产生一个数据框

       long      lat group order         region subregion
1 -79.53800 35.84424  1857 54915 north carolina  alamance
2 -79.54372 35.89008  1857 54916 north carolina  alamance
3 -79.53800 35.98175  1857 54917 north carolina  alamance
4 -79.52081 36.23385  1857 54918 north carolina  alamance
5 -79.26298 36.23385  1857 54919 north carolina  alamance
6 -79.27444 35.90726  1857 54920 north carolina  alamance

仅绘制县（注意：这将是您的邮政编码级别）。 为了解释层继承的原理，我在层调用中“设置”了所有参数（即geom_polygon()）：

ggplot() + 
  geom_polygon(data = counties
              , aes(x = long, y = lat, group = group)  # aesthetic mapping
              , color = "white"                        # fixed value for "line"
              , fill = "lightblue")                    # fixed value for "fill"

如果您现在添加geom_path() 图层而不赋予其美感，则情节不会改变。检查我是否将颜色设置为蓝色，将线条大小设置为 2 以用于演示目的。

ggplot() + 
  geom_polygon(data = counties, aes(x = long, y = lat, group = group), colour = "white", fill = "lightblue") + 
# ---------------- adding a layer with no aesthetics -----------
  geom_path(color = "blue", size = 2)  # ... no joy!

如果您现在将数据和美学移动到ggplot()“base”-layer，路径也将继承美学。在这种情况下，路径将绘制分组纬度/经度位置的“轮廓”。 geom_path() 的层顺序和颜色/大小将“覆盖”白色多边形线。

ggplot(data = counties, aes(x = long, y = lat, group = group)) + 
  geom_polygon( colour = "white", fill = "lightblue") + 
#------------ path layer with inherited "polygon" grouping
  geom_path(color = "blue", size = 2) 

接下来让我们通过平均不同多边形段点的纬度/经度值来创建（邮政编码:)）又名文本标签。

cnames <- counties %>% 
   group_by(subregion) %>% 
   summarise(long = mean(long), lat = mean(lat) # averaging for "mid"-point
)
> cnames
# A tibble: 100 x 3
   subregion  long   lat
   <chr>     <dbl> <dbl>
 1 alamance  -79.4  36.0
 2 alexander -81.2  35.9
 3 alleghany -81.1  36.5

现在添加一个geom_text() 层以显示（邮政编码）又名子区域名称。

ggplot(data = counties, aes(x = long, y = lat, group = group)) + 
   geom_polygon( colour = "white", fill = "lightblue") + 
   geom_path(color = "blue", size = 2) +
# --------------- adding a geom_text() layer 
   geom_text(data = cnames, aes(x = long, y = lat), color = "green")
## ------- uuummmppfff throws an error
Error in FUN(X[[i]], ...) : object 'group' not found

这会引发错误。那为什么呢？ ggplot() 调用中的群体美学隐含地被 geom_polygon() 和 geom_path() 理解......但是 geom_text() 存在问题。

将组美学移动到多边形层...

ggplot(data = counties, aes(x = long, y = lat)) + 
    geom_polygon( aes(group=group), colour = "white", fill = "lightblue") + 
    geom_path(color = "blue", size = 2) + 
    geom_text(data = cnames, aes(x = long, y = lat, label = "subregion"), color = "green")

成功了，但破坏了 geom_path() 层。
这里发生的情况是数据点（即纬度/经度）不再分组，并且 ggplot 按照它们在县数据框中出现的顺序连接端点。这些是您在整个情节中看到的曲线。

因此，您需要为 geom_path 层添加另一个 aes(group=group)！ ...假设您真的想要轮廓的路径。

ggplot(data = counties, aes(x = long, y = lat)) + 
    geom_polygon( aes(group=group), colour = "white", fill = "lightblue") + 
    geom_path(aes(group=group), color = "blue", size = 2) + 
    geom_text(data = cnames, aes(x = long, y = lat, label = "subregion"), color = "green")

显然color = "white" 被geom_path() 调用覆盖。您可以跳过其中一个。

根据经验，ggplot 适用于“长”数据表。添加第二个（或更多其他数据对象）的那一刻，请确保跟踪需要和/或从一层继承到另一层的美学。在您的原始示例中，您可以将 geom_path() 向上移动以从 geom_polygon() 调用中获得 group = group 美学。
如有疑问，请始终在跨层组合（和继承）参数之前为每一层填充 data = ... 和 aes()。

祝你好运！