从一组状态创建区域纬度、长数据框 [英] Create regional lat, long dataframe from group of states

问题描述

我一直在使用 urbnmapr 制作我的所有地图，它包含用于绘制美国各州的漂亮边界.我现在需要几个州的外边界来制作区域地图，并且正在寻找一种方法来过滤数据框以仅包含外边界.

I have been using urbnmapr for all of my mapmaking and it contains nice borders for mapping US states. I now need the outer border of a few states to make a regional map and am looking for a way to filter the dataframe to include only the outer borders.

我将使用此外边框来屏蔽光栅图像.我工作的地区是

I will use this outer border to mask a raster image. The region I am working with is

filter(urbnmapr::states, state_name %in% c("South Dakota", "Nebraska", "Iowa", "Minnesota",
                                              "Missouri", "Michigan", "Indiana", "Illinois",
                                              "Wisconsin", "Kansas", "Ohio", "North Dakota"))

接受任何能给我一个对象的想法，我可以用它来掩盖该区域的栅格.

Open to any ideas that will give me an object I can use to mask a raster of this region.

推荐答案

使用 urbnmapr 和 sf.

在仅您想要的状态的 sf 对象上使用 st_union() 将为您提供外部边界.

Using st_union() on the sf object of only the states you want will give you the exterior borders.

我认为 sf 对象可用于遮罩/裁剪光栅对象.

I think sf objects can be used to mask/crop raster objects.

library(urbnmapr)
library(tidyverse)
library(sf)
#> Linking to GEOS 3.8.0, GDAL 3.0.4, PROJ 6.3.1

states_all <- get_urbn_map(map = 'states', sf = TRUE)
my_states_vec <-  c("South Dakota", "Nebraska", "Iowa", "Minnesota",
                                           "Missouri", "Michigan", "Indiana", "Illinois",
                                           "Wisconsin", "Kansas", "Ohio", "North Dakota")
my_states <- states_all %>% 
  filter(state_name %in% my_states_vec) %>%
  st_union()

head(my_states)
#> Geometry set for 1 feature 
#> geometry type:  MULTIPOLYGON
#> dimension:      XY
#> bbox:           xmin: -340177.8 ymin: -950695.4 xmax: 1627432 ymax: 498098.3
#> projected CRS:  US National Atlas Equal Area
#> MULTIPOLYGON (((1422979 -227154.2, 1423979 -225...

ggplot(my_states) + 
  geom_sf(fill = NA)

^{由 reprex 包 (v0.3.0) 于 2020 年 12 月 10 日创建}

^{Created on 2020-12-10 by the reprex package (v0.3.0)}

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