In sf, how do you identify the geometry type for the sf object as a whole?

[davidhodge931]

In sf, how do you identify the geometry type for the sf object as a whole?

I don't want the geometry type of each feature. Instead at the top when you print a sf object, it says the geometry type as a whole. I want to retreive this.

Any ideas much appreciated!

nc <- sf::st_read(system.file("shape/nc.shp", package = "sf"), quiet = TRUE)

nc
#> Simple feature collection with 100 features and 14 fields
#> Geometry type: MULTIPOLYGON
#> Dimension:     XY
#> Bounding box:  xmin: -84.32385 ymin: 33.88199 xmax: -75.45698 ymax: 36.58965
#> Geodetic CRS:  NAD27
#> First 10 features:
#>     AREA PERIMETER CNTY_ CNTY_ID        NAME  FIPS FIPSNO CRESS_ID BIR74 SID74
#> 1  0.114     1.442  1825    1825        Ashe 37009  37009        5  1091     1
#> 2  0.061     1.231  1827    1827   Alleghany 37005  37005        3   487     0
#> 3  0.143     1.630  1828    1828       Surry 37171  37171       86  3188     5
#> 4  0.070     2.968  1831    1831   Currituck 37053  37053       27   508     1
#> 5  0.153     2.206  1832    1832 Northampton 37131  37131       66  1421     9
#> 6  0.097     1.670  1833    1833    Hertford 37091  37091       46  1452     7
#> 7  0.062     1.547  1834    1834      Camden 37029  37029       15   286     0
#> 8  0.091     1.284  1835    1835       Gates 37073  37073       37   420     0
#> 9  0.118     1.421  1836    1836      Warren 37185  37185       93   968     4
#> 10 0.124     1.428  1837    1837      Stokes 37169  37169       85  1612     1
#>    NWBIR74 BIR79 SID79 NWBIR79                       geometry
#> 1       10  1364     0      19 MULTIPOLYGON (((-81.47276 3...
#> 2       10   542     3      12 MULTIPOLYGON (((-81.23989 3...
#> 3      208  3616     6     260 MULTIPOLYGON (((-80.45634 3...
#> 4      123   830     2     145 MULTIPOLYGON (((-76.00897 3...
#> 5     1066  1606     3    1197 MULTIPOLYGON (((-77.21767 3...
#> 6      954  1838     5    1237 MULTIPOLYGON (((-76.74506 3...
#> 7      115   350     2     139 MULTIPOLYGON (((-76.00897 3...
#> 8      254   594     2     371 MULTIPOLYGON (((-76.56251 3...
#> 9      748  1190     2     844 MULTIPOLYGON (((-78.30876 3...
#> 10     160  2038     5     176 MULTIPOLYGON (((-80.02567 3...

^{Created on 2023-06-12 with reprex v2.0.2}

[technocrat]

library(sf)
#> Linking to GEOS 3.10.2, GDAL 3.4.1, PROJ 8.2.1; sf_use_s2() is TRUE
nc <- st_read(system.file("shape/nc.shp", package="sf"))
#> Reading layer `nc' from data source 
#>   `/home/roc/R/x86_64-pc-linux-gnu-library/4.3/sf/shape/nc.shp' 
#>   using driver `ESRI Shapefile'
#> Simple feature collection with 100 features and 14 fields
#> Geometry type: MULTIPOLYGON
#> Dimension:     XY
#> Bounding box:  xmin: -84.32385 ymin: 33.88199 xmax: -75.45698 ymax: 36.58965
#> Geodetic CRS:  NAD27
u <- st_union(nc)
plot(u)

^{Created on 2023-06-11 with reprex v2.0.2}

[davidhodge931]

Thanks!

I am interested in how you retreive in functionally from an sf object what geometry type it is as a whole.

I know you can do this at a feature level with sf::st_geometry_type. But I am not sure how to do this as a whole through a function?

[technocrat]

An sf object is a collection of one or more geometry features. In one sense the “whole” is the sf itself. In another sense, if we conceptualize it as a set of geometry features the return value of st_union() is the whole. Do you have a different sense in mind?

[davidhodge931]

@technocrat

n another sense, if we conceptualize it as a set of geometry features the return value of st_union() is the

I'm interested in retreiving the value highlighted here when I print the an sf object.

[williaml]

Return geometry type of an object — st_geometry_type • sf (r-spatial.github.io)

library(sf)

nc <- st_read(system.file("shape/nc.shp", package = "sf"), quiet = TRUE)

st_geometry_type(nc)

# [1] MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON
# [15] MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON
# [29] MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON
# [43] MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON
# [57] MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON
# [71] MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON
# [85] MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON MULTIPOLYGON
# [99] MULTIPOLYGON MULTIPOLYGON
# 18 Levels: GEOMETRY POINT LINESTRING POLYGON MULTIPOINT MULTILINESTRING MULTIPOLYGON GEOMETRYCOLLECTION CIRCULARSTRING COMPOUNDCURVE CURVEPOLYGON MULTICURVE MULTISURFACE CURVE ... TRIANGLE

[technocrat]

The closest I see is

library(sf)
#> Linking to GEOS 3.10.2, GDAL 3.4.1, PROJ 8.2.1; sf_use_s2() is TRUE
nc <- st_read(system.file("shape/nc.shp", package="sf"))
#> Reading layer `nc' from data source 
#>   `/home/roc/R/x86_64-pc-linux-gnu-library/4.3/sf/shape/nc.shp' 
#>   using driver `ESRI Shapefile'
#> Simple feature collection with 100 features and 14 fields
#> Geometry type: MULTIPOLYGON
#> Dimension:     XY
#> Bounding box:  xmin: -84.32385 ymin: 33.88199 xmax: -75.45698 ymax: 36.58965
#> Geodetic CRS:  NAD27
attributes(st_geometry(nc))$class
#> [1] "sfc_MULTIPOLYGON" "sfc"

It's also worthwhile reviewing the vignette.