How do you convert from a multipolygon to a spatial polygons data frame

Question

How do you convert from a MULTIPOLYGON to a SpatialPolygonsDataFrame in R?

I can't find any other resources online and I attempted to discretise the same file that was a GEOMETRYCOLLECTION, XY and sfg class, however, this led to a continuous loop of referencing the same polygon without accessing the individual points. I'm happy to provide any additional clarification and will appreciate any insight.

A sample of one of the outputs for the multipolygon Ref_circles to show formatting is given as:

Ref_circles[1]
[[1]]
[[1]][[1]]
       [,1]     [,2]
[1,] 51.62730 4.340600
[2,] 51.62549 4.343550
[3,] 51.61800 4.357353
[4,] 51.61124 4.371529
[5,] 51.60523 4.386039
[6,] 51.59998 4.400845
...
[311,] 51.63570 4.322473
[312,] 51.62894 4.336649
[313,] 51.62730 4.340600

SymbolixAU · Accepted Answer · 2021-03-01 21:23:31Z

7

My first question to you would be: why do you want to convert from an sf object (MULTIPOLYGON) to an sp object (SpatialPolygonDataFrame), as sf supersedes sp?

There are probably ways to achieve your end goal staying within the sf library without having to do this conversion.

If you still want to do it, it will be along the lines of

library(sf)
library(sp)

## using a MULTIPOLYGON data set supplied with library(sf)
nc <- sf::st_read(system.file("shape/nc.shp", package="sf"))

## convert the geometry of the `sf` object to SpatialPolygons
spd <- sf::as_Spatial(st_geometry(nc), IDs = as.character(1:nrow(nc)))

class(spd)
# [1] "SpatialPolygons"
# attr(,"package")
# [1] "sp"

## grab the data from the sf object
df <- nc
df$geometry <- NULL
df <- as.data.frame(df)

## create the SpatialPolygonsDataFrame
spd <- sp::SpatialPolygonsDataFrame(spd, data = df)

class(spd)
# [1] "SpatialPolygonsDataFrame"
# attr(,"package")
# [1] "sp"

head(spd@data)
# AREA PERIMETER CNTY_ CNTY_ID        NAME  FIPS FIPSNO CRESS_ID BIR74 SID74 NWBIR74 BIR79 SID79 NWBIR79
# 1 0.114     1.442  1825    1825        Ashe 37009  37009        5  1091     1      10  1364     0      19
# 2 0.061     1.231  1827    1827   Alleghany 37005  37005        3   487     0      10   542     3      12
# 3 0.143     1.630  1828    1828       Surry 37171  37171       86  3188     5     208  3616     6     260
# 4 0.070     2.968  1831    1831   Currituck 37053  37053       27   508     1     123   830     2     145
# 5 0.153     2.206  1832    1832 Northampton 37131  37131       66  1421     9    1066  1606     3    1197
# 6 0.097     1.670  1833    1833    Hertford 37091  37091       46  1452     7     954  1838     5    1237

edited Mar 1, 2021 at 21:23

answered Jan 29, 2018 at 23:30

SymbolixAU

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AlwaysInTheDark Over a year ago

I'm currently trying to find the area of overlap between a series of circles that I setup using st_buffer(References_coord, dist = 0.3), and a Voronoi diagram generated using st_voronoi(Hubs_coord). For some reason when using st_intersection there is no output area and so I'm trying to use the intersect function, which requires an sp format. I know it seems contrived but it's a problem I've been struggling to deal with gis.stackexchange.com/questions/269498/…

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