Changelog

geoscales 0.1.0.9000

First working version: the Geoscale class, the conversion verb, navigation, plotting, and the Natural Earth provider.

Geoscale, an S7 class holding leaves (one row per atom, one column per level), levels (ordered coarsest first), members (code vocabulary per level), optional geometry, and meta. Everything derivable is computed on demand; nothing is cached on the object.
Three construction layers: geoscale_from_leaves() (escape hatch), geoscale_build() (from parent-child crosswalks — ragged, not Cartesian, because ragged hierarchies are the norm in space), and geoscale_from_provider().
geoscale_example(), a synthetic fixture reproducing three awkward features of real region tables: a code reused at several levels, a cross-cutting level pair, and an atom with no code at any coarser level.

geo_recast() — aggregation and disaggregation as a single operation. Source values are projected down to atoms and then aggregated up to the target, so direction falls out of the level ranks and cross-cutting levels work without special handling.
Rules sum, weighted_mean, mean and copy, each defined in both directions.
geo_register_rule() / geo_get_rule() / geo_list_rules() — a per-parameter rule registry, with an explicit rule= always taking precedence.
na_action = "drop" | "error" | "keep" for partial coverage. "drop" genuinely loses the uncovered share and warns with a count; "keep" conserves totals into an explicit NA group.
Identifier columns are preserved as grouping columns, so panel data converts in one call.

geo_children(), geo_parents(), geo_descendants(), geo_ancestors(), geo_regions(), geo_filter(), geo_prune(), geo_share() and [.
level is a required argument throughout: region codes are not unique across levels, so a bare code is ambiguous.
geo_family(), geo_ancestry() and geo_nests(). Ancestry is computed atom-mediated rather than as a transitive closure — closing over a cross-cutting level would manufacture false relationships.

geo_attach_geometry(), geo_geometry() (dissolve to a level) and geo_area(). sf is in Suggests; the core is geometry-free.
geo_autoplot() draws the hierarchy as an icicle and needs no geometry; geo_plot() draws a choropleth when geometry is attached. geo_layout() exposes the rectangle coordinates for other plotting systems.

geo_register_provider() / geo_provider() / geo_list_providers().
Natural Earth via ne_source() and ne_geoscale(), with source and scale recorded in meta. The package ships no maps and selects no boundaries.
Three Natural Earth pitfalls are handled: adm0_a3 is used as the join key (iso_a3 is -99 for five countries at 1:110m); area weights are refused at scale 110 with a warning; and -99 is converted to NA in numeric attributes as well as code columns.