Geojson to sfc

Extracts geometries from GeoJSON and returns an `sfc` object

geojson_sfc(
  geojson,
  expand_geometries = FALSE,
  input = NULL,
  wkt = NULL,
  crs = NULL,
  proj4string = NULL,
  buffer_size = 1024
)

Arguments

geojson

string or vector of GeoJSON, or a URL or file pointing to a geojson file

expand_geometries

logical indicating whether to unnest GEOMETRYCOLLECTION rows. see details

input

user input for coordinate reference system object

wkt

well-known text for coordinate reference system object

crs

deprecated. coordinate reference system. See Details

proj4string

deprecated. proj4string. See Details

buffer_size

size of buffer used when reading a file from disk. Defaults 1024

Details

specifying expand_geometries = TRUE will expand individual GEOMETRYCOLLECTION geometries to their own row in the resulting `sf` object. If the geometries are part of a Feature (i.e., with properties), the properties will be repeated on each row.

The GEOMETRYCOLLECTION information is not kept when using expand_geometries = TRUE. Therefore, it is not possible to reconstruct the GEOMETRYCOLLECTION after unnesting it.

Geojson specification RFC7946 https://tools.ietf.org/html/rfc7946#page-12 says all CRS should be the World Geodetic System 1984 (WGS 84) [WGS84] datum, with longitude and latitude units of decimal degrees. This is equivalent to the coordinate reference system identified by the Open Geospatial Consortium (OGC) URN urn:ogc:def:crs:OGC::CRS84

geojson_sfc and geojson_sf automatically set the CRS to WGS 84. The fields input and wkt let you to overwrite the defaults.

Examples

## character string of GeoJSON

## load 'sf' for print methods
# library(sf)
geojson <- '{ "type":"Point","coordinates":[0,0] }'
geojson_sfc(geojson)
#> [[1]]
#> [1] 0 0
#> attr(,"class")
#> [1] "XY"    "POINT" "sfg"  
#> 
#> attr(,"n_empty")
#> [1] 0
#> attr(,"crs")
#> $input
#> [1] "4326"
#> 
#> $wkt
#> [1] "GEOGCS[\"WGS 84\",\n      DATUM[\"WGS_1984\",\n        SPHEROID[\"WGS 84\",6378137,298.257223563,\n          AUTHORITY[\"EPSG\",\"7030\"]],\n        AUTHORITY[\"EPSG\",\"6326\"]],\n      PRIMEM[\"Greenwich\",0,\n        AUTHORITY[\"EPSG\",\"8901\"]],\n      UNIT[\"degree\",0.0174532925199433,\n        AUTHORITY[\"EPSG\",\"9122\"]],\n      AXIS[\"Latitude\",NORTH],\n      AXIS[\"Longitude\",EAST],\n    AUTHORITY[\"EPSG\",\"4326\"]]"
#> 
#> attr(,"class")
#> [1] "crs"
#> attr(,"class")
#> [1] "sfc_POINT" "sfc"      
#> attr(,"precision")
#> [1] 0
#> attr(,"bbox")
#> xmin ymin xmax ymax 
#>    0    0    0    0 
#> attr(,"class")
#> [1] "bbox"

geojson <- '[
  { "type":"Point","coordinates":[0,0]},
  {"type":"LineString","coordinates":[[0,0],[1,1]]}
  ]'
geojson_sfc( geojson )
#> [[1]]
#> [1] 0 0
#> attr(,"class")
#> [1] "XY"    "POINT" "sfg"  
#> 
#> [[2]]
#>      [,1] [,2]
#> [1,]    0    0
#> [2,]    1    1
#> attr(,"class")
#> [1] "XY"         "LINESTRING" "sfg"       
#> 
#> attr(,"classes")
#> [1] "POINT"      "LINESTRING"
#> attr(,"n_empty")
#> [1] 0
#> attr(,"crs")
#> $input
#> [1] "4326"
#> 
#> $wkt
#> [1] "GEOGCS[\"WGS 84\",\n      DATUM[\"WGS_1984\",\n        SPHEROID[\"WGS 84\",6378137,298.257223563,\n          AUTHORITY[\"EPSG\",\"7030\"]],\n        AUTHORITY[\"EPSG\",\"6326\"]],\n      PRIMEM[\"Greenwich\",0,\n        AUTHORITY[\"EPSG\",\"8901\"]],\n      UNIT[\"degree\",0.0174532925199433,\n        AUTHORITY[\"EPSG\",\"9122\"]],\n      AXIS[\"Latitude\",NORTH],\n      AXIS[\"Longitude\",EAST],\n    AUTHORITY[\"EPSG\",\"4326\"]]"
#> 
#> attr(,"class")
#> [1] "crs"
#> attr(,"class")
#> [1] "sfc_GEOMETRY" "sfc"         
#> attr(,"precision")
#> [1] 0
#> attr(,"bbox")
#> xmin ymin xmax ymax 
#>    0    0    1    1 
#> attr(,"class")
#> [1] "bbox"

if (FALSE) { # \dontrun{
## GeoJSON at a url
myurl <- "http://eric.clst.org/assets/wiki/uploads/Stuff/gz_2010_us_050_00_500k.json"
sf <- geojson_sfc(myurl)
} # }