calc_catchment_sum: Calculate summary statistics for catchment area.

Description Usage Arguments Details Examples

View source: R/catchmentArea.R

Description

Calculate summary statistics for catchment area.

Usage

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calc_catchment_sum(polygonlayer, targetlayer, calccols, distance = 500,
  projection = paste0("+proj=aea +lat_1=90 +lat_2=-18.416667",
  " +lat_0=0 +lon_0=10 +x_0=0 +y_0=0",
  " +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs"),
  retainAreaProportion = FALSE, quadsegs = NA)

Arguments

polygonlayer

A SpatialPolygonsDataFrame containing zones from which the summary statistics for the catchment variable will be calculated. Smaller polygons will increase the accuracy of the results.

targetlayer

A SpatialPolygonsDataFrame, SpatialLinesDataFrame, SpatialPointsDataFrame, SpatialPolygons, SpatialLines or SpatialPoints object containing the specifications of the facility for which the catchment area is being calculated. If the object contains more than one facility (e.g., multiple cycle paths) the aggregate catchment area will be calculated.

calccols

A vector of column names containing the variables in the polygonlayer to be used in the calculation of the summary statistics for the catchment area.

distance

Defines the size of the catchment area as the distance around the targetlayer in the units of the projection (default = 500 metres)

projection

The proj4string used to define the projection to be used for calculating the catchment areas or a character string 'austalbers' to use the Australian Albers Equal Area projection. Ignored if the polygonlayer is projected in which case the targetlayer will be converted to the projection used by the polygonlayer. In all cases the resulting object will be reprojected to the original coordinate system and projection of the polygon layer. Default is an Albers Equal Area projection but for more reliable results should use a local projection (e.g., Australian Albers Equal Area project).

retainAreaProportion

Boolean value. If TRUE retains a variable in the resulting SpatialPolygonsDataFrame containing the proportion of the original area within the catchment area (Default = FALSE).

quadsegs

Number of line segments to use to approximate a quarter circle. Parameter passed to buffer functions, default is 5 for sp and 30 for sf.

Details

Calculates the summary statistics for a catchment area of a facility (e.g., cycle path) using straight-line distance from variables available in a SpatialPolygonsDataFrame with census tracts or other zones. Assumes that the frequency of the variable is evenly distributed throughout the zone. Returns either a single value if calccols is of length = 1, or a named vector otherwise.

Examples

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## Not run: 
data_dir <- system.file("extdata", package = "stplanr")
unzip(file.path(data_dir, 'smallsa1.zip'))
unzip(file.path(data_dir, 'testcycleway.zip'))
sa1income <- readOGR(".","smallsa1")
testcycleway <- readOGR(".","testcycleway")
calc_catchment_sum(
   polygonlayer = sa1income,
   targetlayer = testcycleway,
   calccols = c('Total'),
   distance = 800,
   projection = 'austalbers'
)

calc_catchment_sum(
polygonlayer = sa1income,
targetlayer = testcycleway,
calccols = c('Total'),
distance = 800,
projection = 'austalbers'
)

## End(Not run)

stplanr documentation built on June 3, 2018, 1:04 a.m.