Skip to contents

Get vectorized Annual NLCD land cover data

get_nlcd_land_cover.Rd

Summarizes Annual National Land Cover Database (NLCD) land cover – a 30-meter categorical raster – to Census tracts (by default) or to a set of user-provided geometries, returning, for each land cover class, both its share of the geometry's area and its area in square meters.

Usage

get_nlcd_land_cover(
  county_geoids = NULL,
  year = 2024,
  geometries = NULL,
  return_raw = FALSE
)

Arguments

county_geoids

A vector of five-character county GEOID(s). Used to fetch tract geometries when geometries is not supplied; ignored when geometries is supplied.

year

One or more years for which to retrieve land cover, each between 1985 and 2024 (the range covered by the Annual NLCD product). Defaults to 2024, the most recent vintage.

geometries

An sf-formatted dataframe specifying the geometries to which NLCD land cover should be summarized. Must contain a GEOID column and have a defined coordinate reference system. Default is NULL, in which case land cover is summarized to Census tracts for the counties named in county_geoids.

return_raw

Logical. If TRUE, the raw (cropped) NLCD raster(s) returned by FedData::get_nlcd_annual() are attached to the result as an attribute named "nlcd_raster".

Value

A tibble with one row per geometry, year, and land cover class present in that geometry:

GEOID

Character. The geometry identifier (tract GEOID, or the GEOID of the supplied geometries).

year

Integer. The NLCD vintage.

land_cover_code

Integer. The NLCD land cover class code (e.g. 11, 21, 42).

land_cover_class

Character. The NLCD class name (e.g. "Open Water", "Deciduous Forest").

area_fraction

Numeric. The coverage-weighted share (0-1) of the geometry's own area falling in this land cover class. A within-geometry proportion – not comparable across geometries on its own; use area_sq_meters for that.

area_sq_meters

Numeric. The absolute area, in square meters, of this record – i.e. of this land cover class within this geometry and year. Comparable across geometries. Sum it by GEOID (optionally with year) to recover a geometry's total area.

When return_raw = TRUE, the raw NLCD rasters (the tibble returned by FedData::get_nlcd_annual(), carrying a rast list-column of SpatRasters) are attached to the result as the "nlcd_raster" attribute.

Details

Land cover is drawn from the Annual NLCD product (Multi-Resolution Land Characteristics Consortium). As of the Collection 1.1 release, Annual NLCD provides a continuous annual time series for the conterminous United States spanning 1985 through 2024. Because land cover is categorical, each geometry is summarized as the coverage-weighted fraction of its area falling in each of the NLCD land cover classes (via exactextractr::exact_extract(fun = "frac")) rather than as a single average value.

The raster download is delegated to FedData::get_nlcd_annual(). Because the Annual NLCD product is currently published only for the conterminous US, Alaska, Hawaii, and the territories are unsupported.

Examples

if (FALSE) { # \dontrun{
# Land cover for every tract in the District of Columbia, 2024
get_nlcd_land_cover(county_geoids = "11001")

# A multi-year panel over a user-supplied set of geometries
geographies = tigris::tracts(state = "24", county = "031", cb = TRUE) %>%
  dplyr::select(GEOID)
get_nlcd_land_cover(geometries = geographies, year = c(2001, 2012, 2024))
} # }