Compare resolution policies

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.

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
  )
}))

Compare resolution policies

Example area

Policies

Tile selection maps

Coverage by policy

Elevation context