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Historical country boundaries

Source: R/time.R
historical_geometry.Rd

Country polygons as they were, from CShapes 2.0 (Schvitz et al. 2022), which maps states and colonies and dependencies for 1886-2019 with per-polygon validity periods. A 1970 map with 2024 borders is a common and quiet error; this is the fix.

Usage

historical_geometry(year, dependencies = FALSE, projection = "equal_earth")

Arguments

year

The year to draw, or a Date for a specific day. CShapes covers 1886-2019.

dependencies

Include colonies and dependencies (default FALSE, matching cshapes). For any pre-decolonisation map you almost certainly want TRUE – most of Africa and Asia is otherwise absent.

projection

Projection to return the geometry in (see world_map()), or NULL for unprojected lon/lat.

Value

An sf frame with gwcode, country, iso3c (where one can be assigned – see below), status, from, to and geometry. Two further CShapes columns are passed through when the installed version supplies them, since they answer the questions this verb is usually asked:

  • owner – the gwcode of the sovereign a dependency belonged to, and NA for a sovereign state. This is the column that makes dependencies = TRUE legible: without it a colony and its metropole are two unrelated rows.

  • capname – the capital's name at that date.

Both were returned but undocumented. Neither is guaranteed: cshapes decides what its own table holds, so check with names() rather than assuming.

The ISO spine does not reach back

ISO 3166 was first published in 1974 and never covered colonies, so a historical map cannot be keyed on iso3c. CShapes uses Gleditsch-Ward codes, which is why gwcode is the key here and iso3c is a best-effort extra: it is NA for every entity that never had an ISO code (French West Africa, the Gold Coast, the USSR before 1974). Join historical data on gwcode, not on iso3c, and use convert_country()(to = "gwn") to get there from a modern code.

References

Schvitz, G., Girardin, L., Ruegger, S., Weidmann, N. B., Cederman, L.-E. & Gleditsch, K. S. (2022). Mapping the international system, 1886-2019: The CShapes 2.0 dataset. Journal of Conflict Resolution 66(1), 144-161. doi:10.1177/00220027211013563

See also

world_geometry(), country_timeline(), world_map()

Examples

if (FALSE) { # \dontrun{
# Africa before decolonisation needs the dependencies
historical_geometry(1950, dependencies = TRUE)
} # }