fix(atlas): give Great Britain its counties and boroughs back

Zooming into England showed nothing below "England" itself, so boroughs
marked as visited had no polygon to light up. It stopped working in 3.1.0,
when the runtime Natural Earth fetch was replaced by the bundled geoBoundaries
assets: Natural Earth carried 232 GB regions including the London boroughs,
and geoBoundaries calls the four constituent countries ADM1. The builder asks
every country for ADM1, so GB shipped as four features.

GB now ships at ADM2 — 216 counties and unitary authorities, which is the
granularity every other country gets from its ADM1 and the granularity that
was there before. That is a deliberate one-country list: ADM2 everywhere
would multiply the bundle for no gain, since ADM1 already is the level people
think in for most countries.

Two things had to be said to data that already exists. Regions marked before
3.1.0 hold the old Natural Earth codes, and are reconciled by name within the
country, the way the 3.1.1 step already does for everywhere else; a row that
still cannot be matched is left alone rather than destroyed. And place_regions
is full of GB-ENG rows that were correct under the old bundle — nothing
re-derives a row that is already cached, so without clearing them every
English place would keep reporting "England" forever.

The bundle guard that would have caught this in 3.1.0 is now in place: four
features for a whole country is not a region layer.

Closes #1974

server/scripts/build-atlas-geo.mjs

@@ -49,6 +49,22 @@ const RETRIES = 3
 // what restores the dropped territories (Greenland, Falklands, French Guiana, …).
 const A3_TO_A2 = {"ABW":"AW", "AFG":"AF", "AGO":"AO", "AIA":"AI", "ALA":"AX", "ALB":"AL", "AND":"AD", "ARE":"AE", "ARG":"AR", "ARM":"AM", "ASM":"AS", "ATA":"AQ", "ATF":"TF", "ATG":"AG", "AUS":"AU", "AUT":"AT", "AZE":"AZ", "BDI":"BI", "BEL":"BE", "BEN":"BJ", "BES":"BQ", "BFA":"BF", "BGD":"BD", "BGR":"BG", "BHR":"BH", "BHS":"BS", "BIH":"BA", "BLM":"BL", "BLR":"BY", "BLZ":"BZ", "BMU":"BM", "BOL":"BO", "BRA":"BR", "BRB":"BB", "BRN":"BN", "BTN":"BT", "BVT":"BV", "BWA":"BW", "CAF":"CF", "CAN":"CA", "CCK":"CC", "CHE":"CH", "CHL":"CL", "CHN":"CN", "CIV":"CI", "CMR":"CM", "COD":"CD", "COG":"CG", "COK":"CK", "COL":"CO", "COM":"KM", "CPV":"CV", "CRI":"CR", "CUB":"CU", "CUW":"CW", "CXR":"CX", "CYM":"KY", "CYP":"CY", "CZE":"CZ", "DEU":"DE", "DJI":"DJ", "DMA":"DM", "DNK":"DK", "DOM":"DO", "DZA":"DZ", "ECU":"EC", "EGY":"EG", "ERI":"ER", "ESH":"EH", "ESP":"ES", "EST":"EE", "ETH":"ET", "FIN":"FI", "FJI":"FJ", "FLK":"FK", "FRA":"FR", "FRO":"FO", "FSM":"FM", "GAB":"GA", "GBR":"GB", "GEO":"GE", "GGY":"GG", "GHA":"GH", "GIB":"GI", "GIN":"GN", "GLP":"GP", "GMB":"GM", "GNB":"GW", "GNQ":"GQ", "GRC":"GR", "GRD":"GD", "GRL":"GL", "GTM":"GT", "GUF":"GF", "GUM":"GU", "GUY":"GY", "HKG":"HK", "HMD":"HM", "HND":"HN", "HRV":"HR", "HTI":"HT", "HUN":"HU", "IDN":"ID", "IMN":"IM", "IND":"IN", "IOT":"IO", "IRL":"IE", "IRN":"IR", "IRQ":"IQ", "ISL":"IS", "ISR":"IL", "ITA":"IT", "JAM":"JM", "JEY":"JE", "JOR":"JO", "JPN":"JP", "KAZ":"KZ", "KEN":"KE", "KGZ":"KG", "KHM":"KH", "KIR":"KI", "KNA":"KN", "KOR":"KR", "KWT":"KW", "LAO":"LA", "LBN":"LB", "LBR":"LR", "LBY":"LY", "LCA":"LC", "LIE":"LI", "LKA":"LK", "LSO":"LS", "LTU":"LT", "LUX":"LU", "LVA":"LV", "MAC":"MO", "MAF":"MF", "MAR":"MA", "MCO":"MC", "MDA":"MD", "MDG":"MG", "MDV":"MV", "MEX":"MX", "MHL":"MH", "MKD":"MK", "MLI":"ML", "MLT":"MT", "MMR":"MM", "MNE":"ME", "MNG":"MN", "MNP":"MP", "MOZ":"MZ", "MRT":"MR", "MSR":"MS", "MTQ":"MQ", "MUS":"MU", "MWI":"MW", "MYS":"MY", "MYT":"YT", "NAM":"NA", "NCL":"NC", "NER":"NE", "NFK":"NF", "NGA":"NG", "NIC":"NI", "NIU":"NU", "NLD":"NL", "NOR":"NO", "NPL":"NP", "NRU":"NR", "NZL":"NZ", "OMN":"OM", "PAK":"PK", "PAN":"PA", "PCN":"PN", "PER":"PE", "PHL":"PH", "PLW":"PW", "PNG":"PG", "POL":"PL", "PRI":"PR", "PRK":"KP", "PRT":"PT", "PRY":"PY", "PSE":"PS", "PYF":"PF", "QAT":"QA", "REU":"RE", "ROU":"RO", "RUS":"RU", "RWA":"RW", "SAU":"SA", "SDN":"SD", "SEN":"SN", "SGP":"SG", "SGS":"GS", "SHN":"SH", "SJM":"SJ", "SLB":"SB", "SLE":"SL", "SLV":"SV", "SMR":"SM", "SOM":"SO", "SPM":"PM", "SRB":"RS", "SSD":"SS", "STP":"ST", "SUR":"SR", "SVK":"SK", "SVN":"SI", "SWE":"SE", "SWZ":"SZ", "SXM":"SX", "SYC":"SC", "SYR":"SY", "TCA":"TC", "TCD":"TD", "TGO":"TG", "THA":"TH", "TJK":"TJ", "TKL":"TK", "TKM":"TM", "TLS":"TL", "TON":"TO", "TTO":"TT", "TUN":"TN", "TUR":"TR", "TUV":"TV", "TWN":"TW", "TZA":"TZ", "UGA":"UG", "UKR":"UA", "UMI":"UM", "URY":"UY", "USA":"US", "UZB":"UZ", "VAT":"VA", "VCT":"VC", "VEN":"VE", "VGB":"VG", "VIR":"VI", "VNM":"VN", "VUT":"VU", "WLF":"WF", "WSM":"WS", "XKX":"XK", "YEM":"YE", "ZAF":"ZA", "ZMB":"ZM", "ZWE":"ZW"}
 
+/**
+ * Countries whose sub-national level is not the one everybody else's ADM1 is.
+ *
+ * geoBoundaries' GBR ADM1 is the four constituent countries — England, Scotland,
+ * Wales, Northern Ireland — so an atlas built from it has no polygon below
+ * "England", and a London borough marked as visited has nothing to light up
+ * (#1974). Its ADM2 is the 216 counties and unitary authorities, which is the
+ * granularity the rest of the world gets from ADM1 and the granularity the
+ * pre-3.1.0 Natural Earth layer had.
+ *
+ * Deliberately a short, hand-picked list. ADM2 everywhere would multiply the
+ * bundle several times over for no gain: for most countries ADM1 already is the
+ * level people think in.
+ */
+const ADM_LEVEL = { GBR: 'ADM2' }
+
 const COUNTRIES = Object.keys(A3_TO_A2) // every ISO alpha-3 code (ADM1 fetch list)
 
 // Cache raw downloads so re-runs (e.g. to tune simplification) don't re-fetch ~360 files.
@@ -216,7 +232,7 @@ async function main() {
 
   // ADM1 (sub-national regions) — per-country gbOpen (carries ISO 3166-2 `shapeISO`).
   console.log('[atlas-geo] downloading ADM1 (regions)…')
-  const adm1Raw = await pool(COUNTRIES, a3 => fetchGeo(MEDIA(a3, 'ADM1')))
+  const adm1Raw = await pool(COUNTRIES, a3 => fetchGeo(MEDIA(a3, ADM_LEVEL[a3] || 'ADM1')))
   const adm1Features = []
   let withCodes = 0
   COUNTRIES.forEach((a3, idx) => {