我正试图计算美国每个普查区的面积。我使用 tidycensus 为每个普查区提取一个带有坐标的多角形。
library(tidycensus)
library(purrr)
census_api_key("KEY")
us <- unique(fips_codes$state)[1:51]
geometry <- map_df(us, function(x) {
get_acs(geography = "tract", variables = "B19013_001", geometry = TRUE,
state = x)
})
我所能找到的计算多角形面积的方法中，没有一种能用列表来计算，而列表是 tidycensus 存储坐标的格式。有没有其他更容易使用的格式？有没有什么方法可以用这种格式的坐标计算面积？
我已经尝试了rgeos包中的gArea()、栅格包中的area()、sf包中的st_area()和几何包中的polyarea()。
使用多边形计算面积。sf::st_area() 对我来说工作正常。下面是一个从以下地方下载数据的例子 tidycensus 并计算佛蒙特州所有普查区的面积。
library(tidycensus)
library(sf)
library(dplyr)
vt_tracts <- get_acs(
geography = "tract",
variables = "B19013_001",
geometry = TRUE,
state = "VT"
)
vt_tracts %>%
mutate(area = st_area(.))
#> Simple feature collection with 184 features and 6 fields
#> geometry type: POLYGON
#> dimension: XY
#> bbox: xmin: -73.43774 ymin: 42.72685 xmax: -71.46455 ymax: 45.01666
#> CRS: 4269
#> First 10 features:
#> GEOID NAME variable estimate
#> 1 50001960100 Census Tract 9601, Addison County, Vermont B19013_001 78750
#> 2 50001960200 Census Tract 9602, Addison County, Vermont B19013_001 74958
#> 3 50001960300 Census Tract 9603, Addison County, Vermont B19013_001 59464
#> 4 50001960400 Census Tract 9604, Addison County, Vermont B19013_001 78672
#> 5 50001960500 Census Tract 9605, Addison County, Vermont B19013_001 56066
#> 6 50001960600 Census Tract 9606, Addison County, Vermont B19013_001 58343
#> 7 50001960700 Census Tract 9607, Addison County, Vermont B19013_001 53910
#> 8 50001960800 Census Tract 9608, Addison County, Vermont B19013_001 66713
#> 9 50001960900 Census Tract 9609, Addison County, Vermont B19013_001 65515
#> 10 50001961000 Census Tract 9610, Addison County, Vermont B19013_001 62763
#> moe geometry area
#> 1 8764 POLYGON ((-73.1968 44.26663... 212702063 [m^2]
#> 2 8731 POLYGON ((-73.39963 44.1553... 158329687 [m^2]
#> 3 10068 POLYGON ((-73.27275 44.1768... 6614856 [m^2]
#> 4 4139 POLYGON ((-73.43774 44.0450... 359804506 [m^2]
#> 5 10897 POLYGON ((-73.1495 44.17669... 109378523 [m^2]
#> 6 3601 POLYGON ((-73.06466 44.0408... 530756434 [m^2]
#> 7 7404 POLYGON ((-73.16763 44.0289... 70741373 [m^2]
#> 8 10440 POLYGON ((-73.19061 44.0189... 30961721 [m^2]
#> 9 4949 POLYGON ((-73.41258 43.9827... 478027734 [m^2]
#> 10 7192 POLYGON ((-73.18767 43.8964... 134156214 [m^2]
虽然要回答你关于寻找美国人口普查区面积的更狭隘的问题，你可以使用 "美国人口普查区"。tigris pacakge (这就是 tidycensus 用来拉动几何体），除了几何体外，它还返回土地面积(ALAND)和水域面积(AWATER)直接从人口普查档案中提取每块土地(或要求的任何其他地理区域)的数据。
tigris::tracts(state = "VT", class = "sf")
#> Simple feature collection with 184 features and 12 fields
#> geometry type: MULTIPOLYGON
#> dimension: XY
#> bbox: xmin: -73.4379 ymin: 42.72693 xmax: -71.46505 ymax: 45.01666
#> CRS: 4269
#> First 10 features:
#> STATEFP COUNTYFP TRACTCE GEOID NAME NAMELSAD MTFCC FUNCSTAT
#> 1 50 007 000600 50007000600 6 Census Tract 6 G5020 S
#> 2 50 007 000800 50007000800 8 Census Tract 8 G5020 S
#> 3 50 007 000900 50007000900 9 Census Tract 9 G5020 S
#> 4 50 007 001100 50007001100 11 Census Tract 11 G5020 S
#> 5 50 001 960400 50001960400 9604 Census Tract 9604 G5020 S
#> 6 50 001 960900 50001960900 9609 Census Tract 9609 G5020 S
#> 7 50 001 960500 50001960500 9605 Census Tract 9605 G5020 S
#> 8 50 001 961000 50001961000 9610 Census Tract 9610 G5020 S
#> 9 50 001 960600 50001960600 9606 Census Tract 9606 G5020 S
#> 10 50 001 960300 50001960300 9603 Census Tract 9603 G5020 S
#> ALAND AWATER INTPTLAT INTPTLON geometry
#> 1 2240206 147061 +44.4833940 -073.1936217 MULTIPOLYGON (((-73.20609 4...
#> 2 1349586 0 +44.4609464 -073.2086195 MULTIPOLYGON (((-73.21524 4...
#> 3 602429 0 +44.4714041 -073.2088310 MULTIPOLYGON (((-73.21393 4...
#> 4 1736310 0 +44.4509355 -073.2197727 MULTIPOLYGON (((-73.23253 4...
#> 5 321773486 38567561 +44.0870615 -073.2671642 MULTIPOLYGON (((-73.43771 4...
#> 6 456817599 21511403 +43.9055842 -073.2904483 MULTIPOLYGON (((-73.41251 4...
#> 7 107525416 1714148 +44.0978095 -073.0485314 MULTIPOLYGON (((-73.1487 44...
#> 8 128778705 5371192 +43.9008582 -073.1035817 MULTIPOLYGON (((-73.18875 4...
#> 9 528821667 1880822 +43.9987500 -072.9398701 MULTIPOLYGON (((-73.06466 4...
#> 10 6413118 203405 +44.1632873 -073.2485362 MULTIPOLYGON (((-73.27275 4...