Query a Feature Service

arc_select() takes a FeatureLayer, Table, of ImageServer object and returns data from the layer as an sf object or data.frame respectively.

Usage

arc_select(
  x,
  ...,
  fields = NULL,
  where = NULL,
  crs = sf::st_crs(x),
  geometry = TRUE,
  filter_geom = NULL,
  predicate = "intersects",
  n_max = Inf,
  page_size = NULL,
  token = arc_token()
)

Arguments

x

an object of class FeatureLayer, Table, or ImageServer.

...

additional query parameters passed to the API.

fields

a character vector of the field names that you wish to be returned. By default all fields are returned.

where

a simple SQL where statement indicating which features should be selected.

crs

the spatial reference to be returned. If the CRS is different than the CRS for the input FeatureLayer, a transformation will occur server-side. Ignored if x is a Table.

geometry

default TRUE. If geometries should be returned. Ignored for Table objects.

filter_geom

an object of class bbox, sfc or sfg used to filter query results based on a predicate function.

predicate

Spatial predicate to use with filter_geom. Default "intersects". Possible options are "intersects", "contains", "crosses", "overlaps", "touches", and "within".

n_max

the maximum number of features to return. By default returns every feature available. Unused at the moment.

page_size

the maximum number of features to return per request. Useful when requests return a 500 error code. See Details.

token

an httr2_token as created by auth_code() or similar

Value

An sf object, or a data.frame

Details

See reference documentation for possible arguments.

FeatureLayers can contain very dense geometries with a lot of coordinates. In those cases, the feature service may time out before all geometries can be returned. To address this issue, we can reduce the number of features returned per each request by reducing the value of the page_size parameter.

arc_select() works by sending a single request that counts the number of features that will be returned by the current query. That number is then used to calculate how many "pages" of responses are needed to fetch all the results. The number of features returned (page size) is set to the maxRecordCount property of the layer by default. However, by setting page_size to be smaller than the maxRecordCount we can return fewer geometries per page and avoid time outs.

Examples

if (FALSE) { # \dontrun{
# define the feature layer url
furl <- paste0(
  "https://services3.arcgis.com/ZvidGQkLaDJxRSJ2/arcgis/rest",
  "/services/PLACES_LocalData_for_BetterHealth/FeatureServer/0"
)

flayer <- arc_open(furl)

arc_select(
  flayer,
  fields = c("StateAbbr", "TotalPopulation")
)

arc_select(
  flayer,
  fields = c("OBJECTID", "PlaceName"),
  where = "TotalPopulation > 1000000"
)
} # }