# Calculate catchment area and associated summary statistics.

Source:`R/catchmentArea.R`

`calc_catchment.Rd`

Calculate catchment area and associated summary statistics.

## Usage

```
calc_catchment(
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,
dissolve = FALSE,
quadsegs = NULL
)
```

## 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. If dissolve = FALSE, all other variables in the original SpatialPolygonsDataFrame for zones that fall partly or entirely within the catchment area will be included in the returned SpatialPolygonsDataFrame but will not be adjusted for the proportion within 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).

- dissolve
Boolean value. If TRUE collapses the underlying zones within the catchment area into a single region with statistics for the whole catchment area.

- 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 catchment area of a facility (e.g., cycle path) using straight-line distance as well as summary statistics 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 a SpatialPolygonsDataFrame.

## See also

Other rnet:
`SpatialLinesNetwork`

,
`calc_catchment_sum()`

,
`calc_moving_catchment()`

,
`calc_network_catchment()`

,
`find_network_nodes()`

,
`gsection()`

,
`islines()`

,
`lineLabels()`

,
`overline_spatial()`

,
`overline()`

,
`plot,SpatialLinesNetwork,ANY-method`

,
`plot,sfNetwork,ANY-method`

,
`rnet_breakup_vertices()`

,
`rnet_group()`

,
`sln2points()`

,
`sum_network_links()`

,
`sum_network_routes()`

## Examples

```
if (FALSE) {
data_dir <- system.file("extdata", package = "stplanr")
unzip(file.path(data_dir, "smallsa1.zip"))
unzip(file.path(data_dir, "testcycleway.zip"))
sa1income <- as(sf::read_sf("smallsa1.shp"), "Spatial")
testcycleway <- as(sf::read_sf("testcycleway.shp"), "Spatial")
cway_catch <- calc_catchment(
polygonlayer = sa1income,
targetlayer = testcycleway,
calccols = c("Total"),
distance = 800,
projection = "austalbers",
dissolve = TRUE
)
plot(sa1income)
plot(cway_catch, add = TRUE, col = "green")
plot(testcycleway, col = "red", add = TRUE)
sa1income <- sf::read_sf("smallsa1.shp")
testcycleway <- sf::read_sf("testcycleway.shp")
f <- list.files(".", "testcycleway|smallsa1")
file.remove(f)
cway_catch <- calc_catchment(
polygonlayer = sa1income,
targetlayer = testcycleway,
calccols = c("Total"),
distance = 800,
projection = "austalbers",
dissolve = TRUE
)
plot(sa1income$geometry)
plot(testcycleway$geometry, col = "red", add = TRUE)
plot(cway_catch["Total"], add = TRUE)
}
```