Compute per-cell area in km²

Returns the area of each cell in square kilometers. For ISEA grids, all cells have the same area (equal-area property). For H3 grids, each cell has a different geodesic area depending on its location.

Usage

cell_area(cell_id = NULL, grid)

Arguments

cell_id

Cell IDs to compute area for. For ISEA grids, these are numeric; for H3 grids, character strings. When grid is a HexData object and cell_id is NULL, all cell IDs from the data are used.

grid

A HexGridInfo or HexData object.

Value

Named numeric vector of areas in km², one per cell_id.

Details

For ISEA grids the area is constant across all cells and is read directly from the grid specification.

For H3 grids the area varies by latitude. This function computes geodesic area via sf::st_area() on H3 cell polygons, with results cached in a session-scoped environment so repeated calls for the same cells are fast.

See also

hex_grid for grid specifications, h3_crosswalk for ISEA/H3 interoperability

Examples

# ISEA: constant area
grid <- hex_grid(area_km2 = 1000)
cells <- lonlat_to_cell(c(0, 10, 20), c(45, 50, 55), grid)
cell_area(cells, grid)

# H3: area varies by location
# \donttest{
h3 <- hex_grid(resolution = 5, type = "h3")
h3_cells <- lonlat_to_cell(c(0, 0), c(0, 80), h3)
cell_area(h3_cells, h3)  # equator vs polar — different areas
# }