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Grid identifiers and neighborhoods

Source: vignettes/grid-utilities.Rmd
grid-utilities.Rmd

PRIO-GRID cell identifiers increase from west to east and then from south to north. The utility functions in this vignette expose that indexing convention and make local neighborhood operations explicit.

Identifier matrices

pg_create_indices() creates a matrix with north at the top, as grids are normally displayed, even though numbering starts in the south-west.

indices <- pg_create_indices(nrow = 3, ncol = 4)
indices
#>      [,1] [,2] [,3] [,4]
#> [1,]    9   10   11   12
#> [2,]    5    6    7    8
#> [3,]    1    2    3    4

The south-western cell is therefore in the bottom-left matrix position.

indices[3, 1]
#> [1] 1
indices[1, 4]
#> [1] 12

First-order neighbors

pg_neighbors() returns queen-contiguity neighbors: cells sharing an edge or a corner with the selected cell.

pg_neighbors(6, nrow = 3, ncol = 4)
#> [1]  9 10 11  5  7  1  2  3

Longitude wraps across the antimeridian by default. Latitude does not wrap across either pole.

pg_neighbors(1, nrow = 3, ncol = 4)
#> [1] 8 5 6 4 2
pg_neighbors(1, nrow = 3, ncol = 4, wrap_longitude = FALSE)
#> [1] 5 6 2

Set wrap_longitude = FALSE for regional grids whose eastern and western edges should not be treated as adjacent.

Connect IDs to locations

For configured grids, pg_coords_from_id() and pg_geometry() translate these abstract identifiers into centre coordinates or spatial features.

config <- priogrid::pg_config(nrow = 18, ncol = 36, verbose = FALSE)

pg_coords_from_id(1:3, config = config)
#>   pgid xcoord ycoord
#> 1    1   -175    -85
#> 2    2   -165    -85
#> 3    3   -155    -85
pg_geometry(1:3, geometry = "point", config = config)
#> Simple feature collection with 3 features and 1 field
#> Geometry type: POINT
#> Dimension:     XY
#> Bounding box:  xmin: -175 ymin: -85 xmax: -155 ymax: -85
#> Geodetic CRS:  +proj=longlat +datum=WGS84 +no_defs
#>   pgid         geometry
#> 1    1 POINT (-175 -85)
#> 2    2 POINT (-165 -85)
#> 3    3 POINT (-155 -85)

See vignette("grid-foundations", package = "priogridR") for coordinate assignment, panel validation, completion, safe joins, and mapping. See vignette("spatial-context", package = "priogridR") for reusable neighbor tables, spatial weights and lags, distance calculations, nearest cells, and buffer summaries.