Layers represent represent a data service hosted by ArcGIS Online, ArcGIS Enterprise, Platform, or even an ArcGIS Hub site. Layers are how you will interact with your remotely hosted data.
The {arcgis} R metapackage is able to work with the most common types
of data services: feature services and image servers. The types of
layers that the R-ArcGIS Bridge does not yet support are vector and map
tile services.
Types of services
When working with these data services, each service type is assigned their own S3 class.
| Class | Description |
|---|---|
FeatureLayer |
Represents vector data. Can contain Point, MultiPoint, Polyline, or Polygon data |
Table |
A type of FeatureLayer in which there is no geometry present. Represents tabular data. |
ImageServer |
Provides access to raster imagery. |
FeatureServer |
A collection of FeatureLayer and Tables. |
GroupLayer |
A collection of FeatureLayer and Tables. |
MapServer |
A collection arbitrary data service types. |
Accessing data services
The R package {arcgislayers} provides access to services. Working with
data services follows a pattern:
- first, create a reference to a remote data service
- query the data service and bring the results back into R
Creating data service objects
Using {arcgislayers}, the function arc_open() will create a
reference to a service based on its url.
library(arcgis)
# feature service url
furl <- "https://services3.arcgis.com/ZvidGQkLaDJxRSJ2/arcgis/rest/services/PLACES_LocalData_for_BetterHealth/FeatureServer/4"
# feature layer
flayer <- arc_open(furl)
flayer#> <FeatureLayer>
#> Name: ZCTAs
#> Geometry Type: esriGeometryPolygon
#> CRS: 3785
#> Capabilities: Query,Extract
Querying feature services
To bring data from the service into memory in R, you must use
arc_select().
Always bring as little data as possible into memory. Utilize the
fields and where arguments.
arc_select(
flayer,
where = "TotalPopulation > 100000",
fields = c("objectid", "totalpopulation", "zcta5")
)#> Warning in CPL_crs_from_input(x): GDAL Message 1: CRS EPSG:3785 is deprecated.
#> Its non-deprecated replacement EPSG:3857 will be used instead. To use the
#> original CRS, set the OSR_USE_NON_DEPRECATED configuration option to NO.
#> Simple feature collection with 23 features and 3 fields
#> Geometry type: POLYGON
#> Dimension: XY
#> Bounding box: xmin: -13584730 ymin: 3464367 xmax: -8218961 ymax: 5130154
#> Projected CRS: WGS 84 / Pseudo-Mercator
#> First 10 features:
#> OBJECTID TotalPopulation ZCTA5 geometry
#> 1 8993 135256 08701 POLYGON ((-8266867 4879638,...
#> 2 10364 100594 92336 POLYGON ((-13081670 4043105...
#> 3 11777 117110 11368 POLYGON ((-8223418 4976558,...
#> 4 11806 109808 77084 POLYGON ((-10655546 3479254...
#> 5 13769 102891 90650 POLYGON ((-13148126 4018344...
#> 6 16570 103660 10467 POLYGON ((-8225085 4996136,...
#> 7 17020 100687 11236 POLYGON ((-8228926 4961496,...
#> 8 17041 103447 11219 POLYGON ((-8239056 4957777,...
#> 9 17068 100883 11385 POLYGON ((-8229187 4970250,...
#> 10 22940 105150 79936 POLYGON ((-11836698 3742458...