Compare resolution policies

This example uses BlueTopo source tiles from the National Bathymetric Source catalog. The build verifies the downloaded assets and records their source metadata.

This example uses BlueTopo tiles covering New York Harbor. The workflow demonstrates tile discovery, checksum-verified asset retrieval, and file-backed raster access with terra. It applies native source-resolution policies to the AOI, reports selected tile coverage, and renders policy footprints. The current New York Harbor example is a compact 4 m native-resolution plan, so policy differences mainly demonstrate selection rules rather than a dramatic visual change.

Smaller meter values mean finer native source resolution. resolution selects source tiles; it does not resample. coverage = "fill" can add fallback source tiles. output_resolution is the argument that changes the output grid.

Example area

Policies

policies <- list(
  native = list(resolution = "native", coverage = "warn"),
  finest = list(resolution = "finest", coverage = "ignore"),
  `finest + coverage fill` = list(resolution = "finest", coverage = "fill"),
  coarsest = list(resolution = "coarsest", coverage = "ignore"),
  `exact available native resolution` = list(resolution = exact_available, coverage = "ignore"),
  `nearest 6 m` = list(resolution = bluertopo_resolution("nearest", value = 6), coverage = "ignore")
)

policy_tiles <- lapply(policies, function(policy) {
  bluertopo_tiles(
    real_aoi,
    resolution = policy$resolution,
    coverage = policy$coverage,
    quiet = TRUE
  )
})

policy_summary <- do.call(rbind, lapply(names(policy_tiles), function(name) {
  tiles <- policy_tiles[[name]]
  df <- as.data.frame(tiles)
  coverage <- attr(tiles, "coverage")
  data.frame(
    policy = name,
    selected_tile_count = nrow(df),
    selected_resolutions = paste(sort(unique(df$resolution_m)), collapse = ", "),
    selected_coverage_fraction = coverage$selected_coverage_fraction,
    selected_aoi_fraction = coverage$selected_aoi_fraction,
    target_met = coverage$target_met,
    stringsAsFactors = FALSE
  )
}))

policy	selected_tile_count	selected_resolutions	Selected coverage (%)	AOI intersected (%)	Target met
Native	2	4	1	1	Yes
finest	2	4	1	1	Yes
finest + coverage fill	2	4	1	1	Yes
coarsest	2	4	1	1	Yes
exact available native resolution	2	4	1	1	Yes
nearest 6 m	2	4	1	1	Yes

Tile selection maps

BlueTopo tile coverage selected under different native source-resolution policies.

Coverage by policy

Coverage fractions selected under different native source-resolution policies.

Use an explicit output grid only when resampling is intended.

Elevation context

BlueTopo bathymetry for New York Harbor, displayed with hillshade, contours, and the example-area boundary.