在ggplot映射中的data_map（）多边形外部删除点

Question

我有以下代码。它绘制了美国的地图。对于这些点，我正在使用一个名为“ x $ osm_points”的对象，但是其中一些点不在美国多边形范围内。我想删除这些内容，只显示美国境内的点。有办法吗？

x $ osm_points看起来像这样

Simple feature collection with 1249248 features and 0 fields
geometry type:  POINT
dimension:      XY
bbox:           xmin: -125.9051 ymin: 24.39989 xmax: -65.243 ymax: 49.38759
CRS:            EPSG:4326
First 10 features:
                     geometry
1  POINT (-80.29432 43.38873)
2  POINT (-80.29536 43.38858)
3    POINT (-80.2953 43.3884)
4  POINT (-80.29515 43.38829)
5   POINT (-80.29497 43.3882)
6  POINT (-80.29481 43.38813)
7  POINT (-80.29458 43.38805)
8  POINT (-80.29436 43.38806)
9  POINT (-80.29415 43.38806)
10 POINT (-80.29402 43.38809)

ggplot代码如下：

ggplot() +
 geom_polygon(data = map_data("usa"), aes(x=long, y = lat, group = group), fill = "black", color = "black", alpha = 1) +
  geom_sf(data = x$osm_points,
          inherit.aes = FALSE,
          colour = "cyan4",
          #fill = "#004529",
          alpha = .1,
          size = 0.5)

谢谢

Answer 1

您可以只将美国数据创建为空间sf对象，然后使用st_intersection裁剪点。

usa <- st_as_sf(map_data('usa'), coords=c('long', 'lat'), crs=4326) %>% 
  st_as_sf(coords = c("Longitude", "Latitude"), crs = 4326) %>%
  group_by(group) %>%
  summarise(geometry = st_combine(geometry)) %>%
  st_cast("POLYGON") %>% 
  st_union()

clipped_points <- st_intersection(x$osm_points, usa)

ggplot() +
  geom_polygon(data = map_data("usa"), aes(x=long, y = lat, group = group),  fill = "black", color = "black", alpha = 1) +
  geom_sf(data = clipped_points,
      inherit.aes = FALSE,
      colour = "cyan4",
      #fill = "#004529",
      alpha = .1,
      size = 0.5)

编辑将x更改为x $ osm_points。 map_data返回剪裁之前必须转换为多边形sf文件的纬度长的多边形坐标。