SpatialPolygons-class function

Class "SpatialPolygons"

class to hold polygon topology (without attributes) class

Objects from the Class

Objects can be created by calls to the function SpatialPolygons

Slots

• polygons:: Object of class "list"; list elements are all of class Polygons-class
• plotOrder:: Object of class "integer"; integer array giving the order in which objects should be plotted
• bbox:: Object of class "matrix"; see Spatial-class
• proj4string:: Object of class "CRS"; see CRS-class

Extends

Class "Spatial", directly.

Methods

Methods defined with class "SpatialPolygons" in the signature:

• [: signature(obj = "SpatialPolygons"): select subset of (sets of) polygons; NAs are not permitted in the row index
• plot: signature(x = "SpatialPolygons", y = "missing"): plot polygons in SpatialPolygons object
• summary: signature(object = "SpatialPolygons"): summarize object
• rbind: signature(object = "SpatialPolygons"): rbind-like method

plot method arguments

The plot method for spatial polygons takes the following arguments:

• x: a SpatialPolygons object
• col: a vector of colour values
• border: default par("fg"); the colour to draw the border
• add: default FALSE; if TRUE, add to existing plot
• xlim, ylim: default NULL; ranges for the plotted x and y values
• xpd: default NULL; controls clipping, see par
• density: default NULL; the density of shading lines, in lines per inch, see polygon
• angle: default 45; the slope of shading lines, given as an angle in degrees (counter-clockwise), see polygon
• pbg: default NULL, set to par("bg") by default transparent ; the colour to paint holes
• axes: default FALSE; draw axes
• lty: default par("lty"); border line type
• ...: other arguments passed through
• setParUsrBB: default FALSE; see Spatial-class for further details
• usePolypath: default NULL to set from option value; use polypath for hole-handling in plot
• rule: default NULL to set from option value; character value specifying the path fill mode, see polypath

The options for usePolypath and rule may be retrieved with get_Polypath (default TRUE on package load) and get_PolypathRule (default winding on package load), and set with set_Polypath and set_PolypathRule

The class definitions used for polygons in sp do not accord with those of the simple features specification of the Open Geospatial Consortium. The rgeos package, an interface to Geometry Engine -- Open Source (GEOS), uses this specification, in which each hole (interior ring) must be associated with its containing exterior ring. In order to avoid introducing incompatible changes into the class definition of Polygons objects, a comment has been added as a single character string to each such object. Here we can trust the data source to assign the hole status correctly, and use round-trip coercion to sf to add such comments to each Polygons member of the polygons slot of this SpatialPolygons object. Exterior rings are coded zero, while interior rings are coded with the 1-based index of the exterior ring to which they belong. SpatialPolygons objects created by reading using sf or terra have the comments set on input, as OGR also uses SFS.

Refer to Bivand et al. (2013), pages 47-48 and 132-133 for a further discussion.

Note

rbind calls the function SpatialPolygons, where it is checked that all IDs are unique. If rbind-ing SpatialPolygons without unique IDs, it is possible to set the argument makeUniqueIDs = TRUE, although it is preferred to change these explicitly with spChFIDs.

References

Roger Bivand, Edzer Pebesma and Virgilio Gomez-Rubio, 2013. Applied spatial data analysis with R, Second edition. Springer, NY. https://asdar-book.org/

Author(s)

Roger Bivand

See Also

SpatialPolygons

Examples

# simple example, from vignette("sp"):
Sr1 = Polygon(cbind(c(2,4,4,1,2),c(2,3,5,4,2)))
Sr2 = Polygon(cbind(c(5,4,2,5),c(2,3,2,2)))
Sr3 = Polygon(cbind(c(4,4,5,10,4),c(5,3,2,5,5)))
Sr4 = Polygon(cbind(c(5,6,6,5,5),c(4,4,3,3,4)), hole = TRUE)

Srs1 = Polygons(list(Sr1), "s1")
Srs2 = Polygons(list(Sr2), "s2")
Srs3 = Polygons(list(Sr3, Sr4), "s3/4")
SpP = SpatialPolygons(list(Srs1,Srs2,Srs3), 1:3)
plot(SpP, col = 1:3, pbg="white")

grd <- GridTopology(c(1,1), c(1,1), c(10,10))
polys <- as(grd, "SpatialPolygons")
plot(polys)
text(coordinates(polys), labels=row.names(polys))