The generic function extractFromLayer uses information from a GIS
shapefile to define node attributes. For each node, information is retrieved
from the layer and assigned to that node.
Usage
extractFromLayer(x, ...)
# S4 method for matrix
extractFromLayer(x, layer = "world", attr = "all", ...)
# S4 method for data.frame
extractFromLayer(x, layer = "world", attr = "all", ...)
# S4 method for list
extractFromLayer(x, layer = "world", attr = "all", ...)
# S4 method for gGraph
extractFromLayer(x, layer = "world", attr = "all", ...)
# S4 method for gData
extractFromLayer(x, layer = "world", attr = "all", ...)Arguments
- x
a matrix, a data.frame, a list, a valid gGraph, or a valid gData object. For matrix and data.frame, input must have two columns giving longitudes and latitudes of locations being considered. For list, input must have two components being vectors giving longitudes and latitudes of locations.
- ...
further arguments to be passed to other methds. Currently not used.
- layer
a shapefile of the class
SpatialPolygonsDataFrame(seereadShapePolyin maptools package to import such data from a GIS shapefile). Alternatively, a character string indicating one shapefile released with geoGraph; currently, only 'world' is available (see?data(worldshape)).- attr
a character vector giving names of the variables to be extracted from the layer. If 'all', all available variables are extracted. In case of problem, available names are displayed with the error message. Available data are also stored in
layer@data.
Value
The output depends on the nature of the input:
- matrix,
data.frame, list: a data.frame with one row per location, and as many
columns as requested variables ('attributes').
gGraph: a gGraph object with new node attributes (@nodes.attrslot). If nodes attributes already existed, new attributes are added as new columns.gData: a gData object with new data associated to locations (@dataslot). New information is merge to older information according to the type of data being stored.
Details
Nodes can be specified in different ways, including by providing a gGraph or a gData object. Outputs match the input formats.
See also
findLand, to find which locations are on land.
Examples
if (FALSE) {
plot(worldgraph.10k, reset = TRUE)
## see what info is available
names(worldshape@data)
unique(worldshape@data$CONTINENT)
## retrieve continent info for all nodes
## (might take a few seconds)
x <- extractFromLayer(worldgraph.10k, layer = worldshape, attr = "CONTINENT")
x
table(getNodesAttr(x, attr.name = "CONTINENT"))
## subset Africa
temp <- getNodesAttr(x, attr.name = "CONTINENT") == "Africa"
temp[is.na(temp)] <- FALSE
x <- x[temp]
plot(x, reset = TRUE)
}