unionSpatialPolygons

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Percentile

Aggregate Polygons in a SpatialPolygons object

The function aggregates Polygons in a SpatialPolygons object, according to the IDs vector specifying which input Polygons belong to which output Polygons; internal boundaries are dissolved using the gpclib package union() function.

Keywords
spatial
Usage
unionSpatialPolygons(SpP, IDs, threshold=NULL)
Arguments
SpP
A SpatialPolygons object as defined in package sp
IDs
A vector defining the output Polygons objects, equal in length to the length of the polygons slot of SpRs; it may be character, integer, or factor (try table(factor(IDs)) for a sanity check)
threshold
if not NULL, an area measure below which slivers will be discarded (some polygons have non-identical boundaries, for instance along rivers, generating slivers on union which are artefacts, not real sub-polygons)
Value

  • Returns an aggregated SpatialPolygons object named with the aggregated IDs values in their sorting order; see the ID values of the output object to view the order.

Aliases
  • unionSpatialPolygons
Examples
library(sp)
library(gpclib)
nc1 <- readShapePoly(system.file("shapes/sids.shp", package="maptools")[1], proj4string=CRS("+proj=longlat +datum=NAD27"))
lps <- coordinates(nc1)
ID <- cut(lps[,1], quantile(lps[,1]), include.lowest=TRUE)
reg4 <- unionSpatialPolygons(nc1, ID)
sapply(slot(reg4, "polygons"), function(i) slot(i, "ID"))
Documentation reproduced from package maptools, version 0.6-19, License: GPL (>= 2)

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