Find the spatial overlap between a raster and a set of polygons
Source:R/overlay_weights.R
overlay_weights.RdThe overlay_weights() function generates a table of weights mapping
each grid cell to its respective polygon(s) for use in the staggregate_*()
family of functions.
Arguments
- polygons
a simple features polygon or multipolygon object
- polygon_id_col
the name of a column in the
polygonsobject with a unique identifier for each polygon- grid
a raster layer with the same spatial resolution as the data
- secondary_weights
an optional table of secondary weights, output from the
secondary_weights()function
Examples
overlay_output_with_secondary_weights <- overlay_weights(
polygons = tigris::counties("nj"), # Polygons outlining the 21 counties of New Jersey
polygon_id_col = "COUNTYFP", # The name of the column with the unique
# county identifiers
grid = era5_grid, # The grid to use when extracting area weights (era5_grid is the
# default)
secondary_weights = cropland_world_2015_era5 # Output from
# secondary_weights
# (cropland_world_2015_era5 is
# available to the# user)
)
#> Checking for raster/polygon alignment
#> Retrieving data for the year 2022
#>
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#> Aligning longitudes to standard coordinates.
#> Extracting raster polygon overlap
#> Secondary weights fully overlap with the administrative regions.
#> Checking sum of weights within polygons
#> All weights sum to 1.
head(overlay_output_with_secondary_weights)
#> x y poly_id w_area weight
#> <num> <num> <char> <num> <num>
#> 1: 284.5 39.25 011 0.017221145 0.033565672
#> 2: 284.5 39.25 033 0.005816417 0.006236843
#> 3: 284.5 39.50 011 0.017033115 0.028784469
#> 4: 284.5 39.50 033 0.355072708 0.330109034
#> 5: 284.5 39.75 015 0.021931677 0.024382703
#> 6: 284.5 39.75 033 0.182386051 0.156198032
overlay_output_without_secondary_weights <- overlay_weights(
polygons = tigris::counties("nj"), # Polygons outlining the 21 counties of New Jersey
polygon_id_col = "COUNTYFP" # The name of the column with the unique county
# identifiers
)
#> Checking for raster/polygon alignment
#> Retrieving data for the year 2022
#> Aligning longitudes to standard coordinates.
#> Extracting raster polygon overlap
#> Checking sum of weights within polygons
#> All weights sum to 1.
head(overlay_output_without_secondary_weights)
#> x y poly_id w_area w_sum
#> <num> <num> <char> <num> <num>
#> 1: 285.00 41.25 037 0.0140156458 1
#> 2: 285.25 41.25 037 0.3241450630 1
#> 3: 285.50 41.25 037 0.2178277183 1
#> 4: 285.75 41.25 037 0.0002487302 1
#> 5: 285.00 41.00 037 0.0470109628 1
#> 6: 285.25 41.00 037 0.3165378806 1