R 如何在具有多个多边形的 shapefile 中合并多边形要素?(可重现的代码示例)

如何在包含多个多边形的 shapefile 中合并多边形要素?

rbind 和 union 只是组合 shapefile 特征的行，它们实际上并没有合并多边形本身.

rbind and union just combine the rows of the shapefile features, they don't actually merge the polygons themselves.

以下示例中的所需结果:

如何将以下具有重复 ID_2 的 shapefile 合并为 sptemp 中的单个多边形?

How do I get the below shapefile with duplicated ID_2 to merge to a single polygon in sptemp?

埃塞俄比亚 GADM 级别 2 的以下示例具有重复的 shapefile ID_2 列的前两行(值 = 1).我想要具有 79 个功能的 sptemp，将前两行(即 ID_2 重复的行)组合在一起.sptemp[1,] 的图会显示当前 sptemp[1,] 和 sptemp2[2,] 的位置，而没有重复之间的边界，即多边形也合并了.

Example below of GADM level 2 of Ethiopia has first two rows of the shapefile ID_2 column duplicated (value=1). I'd like sptemp with 79 features combining the first two rows that are the ones with duplicated ID_2. A plot of sptemp[1,] would bring up where current sptemp[1,] and sptemp2[2,] without the boundaries between the duplicated, i.e. the polygons are merged too.

示例代码:

下载、解压并加载到埃塞俄比亚 2 级的 R GADM 文件(899kb 到工作目录):

Download, unzip, and load into R GADM file for Ethiopia level 2 (899kb to working directory):

library(curl)
library(rgdal)

curl_download("http://biogeo.ucdavis.edu/data/gadm2.8/shp/ETH_adm_shp.zip",
              destfile=paste0("gadmETH.zip"),
              quiet=FALSE)

unzip(paste0("gadmETH.zip"), exdir="gadmETH", overwrite=FALSE) 


###Load shapefile
sptemp <- readOGR(dsn="gadmETH", layer="ETH_adm2")

前两个多边形的 ID_2 列重复

The ID_2 column for the first two polygons is duplicated

###You'll see in the first two rows ID_2 is duplicated
df.sptemp <- as.data.frame(sptemp)

View(sptemp)

###I can't just delete one because they are separate polygons 
plot(sptemp[1,], col="blue")
plot(sptemp[2,], add=TRUE, col="red" )