shapefile多边形的ggplot2 facet图产生奇怪的线条

Question

我正在努力制作一个等值线图的构面/点阵图，每个图都显示不同的模型运行如何影响一个变量被映射到多个多边形。问题是输出图形会在每个图中的多边形之间产生奇怪的线条（参见下图）。

虽然我已经将shapefile操作并转换为具有ggplot2的适当属性的数据框，但我不熟悉如何使用该包的详细信息，并且在线文档仅限于这样一个复杂的包。我不确定是什么参数导致了这个问题，但我怀疑它可能是aes参数。

剧本：

library(rgdal, tidyr, maptools, ggplot2, dplyr, reshape2)

setwd('D:/path/to/wd')

waterloo <- read.table("waterloo-data.txt", header=TRUE, sep=',', stringsAsFactors=FALSE)
waterloo <- data.frame(waterloo$DAUID, waterloo$LA0km, waterloo$LA4_exp, waterloo$LA20km, waterloo$LA30km, waterloo$LA40km, waterloo$LA50km)
colnames(waterloo) <- c("DAUID", "LA0km", "LA10km","LA20km", "LA30km", "LA40km", "LA50km")

## Produces expenditure measurements by ID variable DAUID, using reshape2/melt
wtidy <- melt(waterloo, id.vars=c("DAUID"), measure.vars = c("LA0km", "LA10km", "LA20km", "LA30km", "LA40km", "LA50km"))
colnames(wtidy) <- c("DAUID", "BufferSize", "Expenditure")

wtidy$DAUID <- as.factor(wtidy$DAUID) # for subsequent join with wtrl_f

### READ SPATIAL DATA ###
#wtrl <- readOGR(".", "Waterloo_DA_2011_new")
wtrl <- readShapeSpatial("Waterloo_DA_2011_new")
wtrl$id <- row.names(wtrl)

wtrl_f <- fortify(wtrl)
wtrl_f <- left_join(wtrl_f, wtrl@data, by="id")

# Join wtrl fortified (wtrl_f) to either twaterloo or wtidy
wtrl_f <- left_join(wtrl_f, wtidy, by="DAUID")

### PLOT SPATIAL DATA ###
ggplot(data = wtrl_f, # the input data
       aes(x = long.x, y = lat.x, fill = Variable/1000, group = BufferSize)) + # define variables
  geom_polygon() + # plot the DAs
  geom_path(colour="black", lwd=0.05) + # polygon borders
  coord_equal() + # fixed x and y scales
  facet_wrap(~ BufferSize, ncol = 2) + # one plot per buffer size
  scale_fill_gradient2(low = "green", mid = "grey", high = "red", # colors
                       midpoint = 10000, name = "Variable\n(thousands)") + # legend options
  theme(axis.text = element_blank(), # change the theme options
        axis.title = element_blank(), # remove axis titles
        axis.ticks = element_blank()) # remove axis ticks

输出图形如下所示：

奇怪！我取得了很好的进展，但我不知道ggplot在哪里获得这些线条。任何有关这方面的帮助将不胜感激！

PS;作为一个额外的无关问题，多边形线条相当锯齿状。我该如何平滑这些线？

Answer 1

这个答案帮助我解决了我的问题，但是在我编写这个准备发布的最小例子之前。我在这里分享它，以防它帮助某人更快地解决同样的问题。

问题： 我正在尝试使用ggplot2在R中制作基本地图。多边形填充错误，形成额外的线条。

library("ggplot2")
library("maps")

map <- ggplot(map_data("world", region = "UK"), aes(x = long, y = lat)) + geom_polygon()
map

wrong map image

解决方案： 我必须设置美学“组”参数以使多边形点按正确顺序排列，否则ggplot将尝试在南海岸中间绘制一片苏格兰海岸线（例如）。

map <- ggplot(map_data("world", region = "UK"), aes(x = long, y = lat, group = group)) + geom_polygon()
map

Answer 2

好的，我设法通过更改ggplot2手册第11页上的美学组参数来解决此问题： http://cran.r-project.org/web/packages/ggplot2/ggplot2.pdf

正确的参数是“group”，而不是用于对图表进行分组的因子。正确的ggplot代码：

    ggplot(data = wtrl_f, # the input data
       aes(x = long.x, y = lat.x, fill = Expenditure/1000, group = group)) + # define variables
  geom_polygon() + # plot the DAs
  geom_path(colour="black", lwd=0.025) + # DA borders
  coord_equal() + # fixed x and y scales
  facet_wrap(~ BufferSize, ncol = 2) + # one plot per buffer size
  scale_fill_gradient2(low = "green", mid = "grey", high = "red", # colors
                       midpoint = 10000, name = "Expenditures\n(thousands)") + # legend options
  theme(axis.text = element_blank(), # change the theme options
        axis.title = element_blank(), # remove axis titles
        axis.ticks = element_blank()) # remove axis ticks