Add OCD-IDs for UK Scottish Parliament, Senedd, wards, and CEDs

identifiers/country-gb/README.md

@@ -1,17 +1,47 @@
 # Open Civic Data Divisions: United Kingdom
 
-This folder list the following divisions of United Kingdom:
+This folder lists the following divisions of the United Kingdom:
 
 * Countries of the United Kingdom [ref](https://en.wikipedia.org/wiki/Countries_of_the_United_Kingdom).
 * Regions of England [ref](https://simple.wikipedia.org/wiki/Regions_of_England).
-* Constituencies of the Parliament of the United Kingdom [ref](https://en.wikipedia.org/wiki/Constituencies_of_the_Parliament_of_the_United_Kingdom).
+* Constituencies of the UK Parliament [ref](https://en.wikipedia.org/wiki/Constituencies_of_the_Parliament_of_the_United_Kingdom).
+* Constituencies and regions of the Scottish Parliament [ref](https://en.wikipedia.org/wiki/Scottish_Parliament_constituencies_and_regions).
+* Constituencies and regions of the Senedd / Welsh Parliament, including the new 16-constituency boundaries effective May 2026 [ref](https://en.wikipedia.org/wiki/Senedd_constituencies_and_electoral_regions).
+* UK-wide electoral wards [ref](https://en.wikipedia.org/wiki/Wards_and_electoral_divisions_of_the_United_Kingdom).
+* English county electoral divisions [ref](https://en.wikipedia.org/wiki/County_electoral_division).
+
+NI Assembly constituencies share boundaries with NI Westminster constituencies post the 2023 OSNI review and so reuse the corresponding `ed:` identifiers.
 
 ## Types
 
-* `part`: Parts
-* `region`: Regions (of England)
-* `ed`: electoral districts
+| Type | Path | Notes |
+|---|---|---|
+| `part` | `country:gb/part:<eng\|sct\|wls\|nir>` | The four parts of the UK. |
+| `region` | `country:gb/part:eng/region:<nuts1>` | NUTS1 regions of England. |
+| `ed` | `country:gb/part:.../ed:<slug>` | Westminster (UK Parliament) constituencies. |
+| `spc` | `country:gb/part:sct/spc:<slug>` | Scottish Parliament constituencies. |
+| `spr` | `country:gb/part:sct/spr:<slug>` | Scottish Parliament regions. |
+| `senc` | `country:gb/part:wls/senc:<slug>` | Senedd / Welsh Parliament constituencies. |
+| `senr` | `country:gb/part:wls/senr:<slug>` | Senedd electoral regions (abolished from May 2026). |
+| `ward` | `country:gb/part:.../ward:<gss>` | Electoral wards UK-wide. |
+| `ced` | `country:gb/part:eng/ced:<gss>` | English county electoral divisions. |
+
+Wards and county electoral divisions key on the canonical [GSS code](https://en.wikipedia.org/wiki/ONS_coding_system) instead of a name slug because UK ward names are not nationally unique (e.g. there are 21 wards named "Castle"). Constituencies and regions, by contrast, have unique names within each type.
+
+The `senc` and `senr` prefixes follow the body's current name (Senedd / Welsh Parliament, post-2020) and match the modern ONS column codes (`senc22cd`, `senr22cd`). The earlier (never-merged) `country-uk` script and the stalled migration in #186 used `nawc` / `nawr` from when the body was the National Assembly for Wales.
+
+A `gss_code` extra column is carried on every row that maps to a single ONS GSS code, mirroring the older `country-uk` files and #186, so consumers can crosswalk OCD-IDs ↔ GSS codes without a separate lookup.
+
+## Open conventions debate
+
+The hierarchy used here (`country:gb/part:<nation>/<type>:<slug>`) matches the current merged state of `constituencies.csv` (most recently extended in #385). It is not the only proposed convention -- see #170, #184, and the stalled #186, which proposed a flat scheme (`country:gb/<type>:<slug>`) on the grounds that nesting a UK-wide Westminster constituency under `part:eng` etc. implies geographic scope it doesn't have. The objection in #184 specifically targets Westminster's hierarchy; for sub-national bodies like the Scottish Parliament and the Senedd, the geographic nesting is truthful. This PR keeps the hierarchy for consistency with `constituencies.csv`, but reviewers should redirect to a flat scheme if that's the preferred direction; the typed prefixes (`spc`, `senc`, etc.) carry the disambiguation either way.
+
+## Sources
+
+* Westminster, Scottish Parliament, Senedd, ward, and CED boundaries: ONS [Open Geography Portal](https://geoportal.statistics.gov.uk/) -- Open Government Licence v3.0.
+* Senedd post-May-2026 constituencies: [DataMapWales](https://datamap.gov.wales/layers/geonode:senedd_final_2026) (Welsh Government, OGL v3.0). The 16 constituencies use placeholder GSS codes of the form `W92000001`-`W92000016` until ONS publishes canonical codes; if those change, the rows in this folder will need a `sameAs` plus a refreshed `gss_code`.
 
 ## Updates
 
-* 2023-07-01: After the 2023 Periodic Review of Westminster constituencies the Parliamentary Constituencies Order 2023 the UK Gov introduced a lot of changes for the next general HoC election. [ref](https://en.wikipedia.org/wiki/2023_Periodic_Review_of_Westminster_constituencies#New_and_abolished_constituencies).
+* 2023-07-01: After the 2023 Periodic Review of Westminster constituencies the Parliamentary Constituencies Order 2023 introduced a lot of changes for the next UK General Election. [ref](https://en.wikipedia.org/wiki/2023_Periodic_Review_of_Westminster_constituencies#New_and_abolished_constituencies).
+* 2026-05-06: Senedd boundaries change. The 40 constituencies + 5 regions are abolished and replaced by 16 new constituencies. Existing `senc:` / `senr:` rows carry `validThrough=2026-05-05`; the new `senc:` rows carry `validFrom=2026-05-06`.