| unionSpatialPolygons {maptools} | R Documentation |
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.
unionSpatialPolygons(SpP, IDs, threshold=NULL)
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) |
Returns an aggregated SpatialPolygons object named with the aggregated IDs values in their sorting order; see getSpPPolygonsIDSlots() of the output object to view the order.
Roger Bivand
library(sp)
library(gpclib)
nc1 <- readShapePoly(system.file("shapes/sids.shp", package="maptools")[1], proj4string=CRS("+proj=longlat +datum=NAD27"))
lps <- getSpPPolygonsLabptSlots(nc1)
ID <- cut(lps[,1], quantile(lps[,1]), include.lowest=TRUE)
reg4 <- unionSpatialPolygons(nc1, ID)
getSpPPolygonsIDSlots(reg4)