R - 合并城市名称以近似经纬坐标

Question

我想将城市名称合并为近似坐标。

我有两个数据集。

1. 城市的经纬度，称为cities。
2. 观测事件的经纬度，称为events。

大多数事件都发生在城市的经纬度之外。

如果经纬度最大 1 lat 和 lon 与 events 中列出的不同，我想从 cities 合并 city。

data.table 中的nearest 函数似乎过于粗糙。

你会怎么做？使用maptools?

例子：

cities <- data.table(city = c("A", "B", "C"),
                 lat = c(23.4, 43.5, 21.3),
                 lon = c(100, 98.4, -78.2))

events <- data.table(event = c("X1", "Y1", "B1"),
                 lat = c(24.4, 42.5, 23.3),
                 lon = c(101, 100.4, -78.2)))

result <- data.table(event = c("X1", "Y1", "B1"),
                 lat = c(23.4, 43.5, 21.3),
                 lon = c(100, 98.4, -78.2),
                 city = c("A", NA, NA))

> result
   event  lat   lon city
1:    X1 23.4 100.0    A
2:    Y1 43.5  98.4 <NA>
3:    B1 21.3 -78.2 <NA>

Answer 1

方法一：非等值连接

这种非 equi 更新连接可以解决问题...但这只有在您设置了硬性 1 度限制后才会起作用。问题是 2 度之间的距离在全球范围内会有所不同......

events[ cities[, `:=`(lat_min = lat - 1, lat_max = lat+1,
                      lon_min = lon - 1, lon_max = lon + 1) ], 
        city := i.city, 
        on = .(lat >= lat_min, lat <= lat_max, lon >= lon_min, lon <= lon_max ) ][]

#    event  lat   lon city
# 1:    X1 24.4 101.0    A
# 2:    Y1 42.5 100.4 <NA>
# 3:    B1 23.3 -78.2 <NA>

方法2：基于绝对距离

如果您想设置事件和城市之间的最大距离，您需要这样的空间解决方案：

#maximum distance between event and city (in metres)
max_dist = 180000

library( sf )
#create simple (point) features of events and cities
cities.sf <- st_as_sf( cities, coords = c("lon", "lat"), crs = 4326 )
events.sf <- st_as_sf( events, coords = c("lon", "lat"), crs = 4326 )

#spatial join
st_join( events.sf, cities.sf, join = st_is_within_distance, dist = max_dist )

# Simple feature collection with 3 features and 2 fields
# geometry type:  POINT
# dimension:      XY
# bbox:           xmin: -78.2 ymin: 23.3 xmax: 101 ymax: 42.5
# CRS:            EPSG:4326
#   event city           geometry
# 1    X1    A   POINT (101 24.4)
# 2    Y1 <NA> POINT (100.4 42.5)
# 3    B1 <NA> POINT (-78.2 23.3)