31:T7c1,header = { const firs100 = firsAt(100).features.filter( (d) => d.properties.type !== "NO_FIR" ); const noFirs = firsAt(100).features.filter( (d) => d.properties.type === "NO_FIR" ); return addTooltips( Plot.carto({ projection: "bertin1953", color: { range: ["url(#crosshatch)", ...colorscale, ...colorscale] }, marks: [ () => // https://github.com/iros/patternfills svg` `, Plot.feature({ type: "Sphere" }, { fill: "white" }), Plot.feature(graticule, { stroke: "#aaa", strokeWidth: 0.25 }), Plot.feature(land, { stroke: "#333", fill: "#ced4da" }), Plot.features(noFirs, { fill: "white" }), Plot.features(noFirs, { fill: (d) => " ", fillOpacity: 0.4, strokeWidth: 1.5, stroke: "#fff", title: (elt) => `No FIR area` }), Plot.features(firs100, { fill: (d) => d.properties.designator[0], fillOpacity: 0.4, strokeWidth: 1.5, stroke: "#fff", title: (d) => `${d.properties.designator}\n${d.properties.name}` }), Plot.feature({ type: "Sphere" }, { stroke: "black", strokeWidth: 2 }), Plot.label( firs100.filter((elt) => d3.geoArea(elt) > 2e-2), { text: (d) => d.properties.designator, halo: true, fontSize: (11 * width) / 960 } ) ], width, height: 0.54 * width }), { "stroke-width": "2px", stroke: "#f58518" } ); }32:T68b,{ function franceMap(fir_uir, width) { const height = width * 0.8; const local_firs = firsAt(fir_uir ? 300 : 100).features.filter( (d) => d.properties.designator.slice(0, 2) === "LF" ); const other_firs = firsAt(fir_uir ? 300 : 100).features.filter( (d) => d.properties.designator.slice(0, 2) !== "LF" && ["E", "L", "D", "U", "G", "H"].includes(d.properties.designator[0]) ); return Plot.carto({ projection: d3 .geoConicConformal() .scale((10 * width) / 1.5 / Math.PI) .rotate([-3, -46.5]) .parallels([49, 44]) .translate([width / 2, height / 2]), color: { scheme: "tableau10", legend: true }, marks: [ Plot.feature(countries, { stroke: "#333", fill: "#ced4da" }), Plot.features( local_firs.filter((x) => x.properties.designator), { fill: (d) => d.properties.designator, fillOpacity: 0.6, strokeWidth: 2, stroke: "#eee" } ), Plot.features(other_firs, { fill: "#bab0ac", fillOpacity: 0.2, strokeWidth: 2, stroke: "#eee" }), Plot.label(local_firs, { text: (d) => `${d.properties.designator}\n${d.properties.name}`, fontSize: (24 * width) / 960, halo: true }) ], width, height, caption: fir_uir ? "Above FL 195" : "Below FL 195" }); } const franceFIR = franceMap(false, width / 2); const franceUIR = franceMap(true, width / 2); return html`

${franceFIR} ${franceUIR}`; }33:Tb2d,{ const rotating_globe = function (rotate, width) { const height = 0.95 * width; return Plot.carto({ projection: "orthographic", rotate: rotate, color: { range: ["url(#crosshatch)", ...colorscale, ...colorscale] }, marks: [ () => svg` `, Plot.feature({ type: "Sphere" }, { fill: "white" }), Plot.feature(graticule, { stroke: "#aaa", strokeWidth: 0.25 }), Plot.feature(land, { stroke: "#333", fill: "#ced4da" }), Plot.features( // hide graticule firsAt(100).features.filter((d) => d.properties.type === "NO_FIR"), { fill: "white" } ), Plot.features( firsAt(100).features.filter((d) => d.properties.type === "NO_FIR"), { fill: (d) => " ", fillOpacity: 0.4 } ), Plot.features(letter_areas, { fill: (d) => d.properties.designator[0], fillOpacity: 0.4, strokeWidth: 1, stroke: "#79706e" //stroke: (d) => d.properties.designator[0] }), Plot.points(airports, { lonLat: (d) => [d.longitude, d.latitude], fill: (d) => d.icao[0], fillOpacity: 0, title: (d) => `${d.icao} / ${d.iata} : ${d.name}\n(${d.country})`, r: 4 }), Plot.points(airports, { lonLat: (d) => [d.longitude, d.latitude], fill: (d) => d.icao[0], stroke: "black", strokeWidth: 0.15, r: 1.4 }), Plot.label(letter_centroids, { lonLat: (d) => d.latlon, fill: (d) => d.letter, // Not sure these two options really help, but maybe the H is more readable with it? stroke: "white", strokeWidth: 4, //fill: "black", halo: true, text: (d) => d.letter, fontSize: (48 * width) / 960 }) ], width, height }); }; const map = rotating_globe([90, -20], width / 3); return html`

${map} ${rotating_globe([-30, -30], width / 3)} ${rotating_globe([-150, -10], width / 3)}

${Plot.legend({ color: { ...map.scale("color"), domain: map.scale("color").domain.filter((d, i) => (i > 0) & (d !== "X")), range: map.scale("color").range.filter((d, i) => (i > 0) & (d !== "X")) }, columns: 7, width: 350, style: { fontSize: "10pt", margin: "2ex" } })}`; }34:T633,- Micronesia, Kiribati, Marshall islands are all in the **North-Eastern Pacific region `P`**, together with Alaska and Hawaii: they are all in the Oakland Oceanic FIR `KZAK`, prefixed the `K` from the United States. Similarly Bermuda is attached to the **Caribbean region `T`** but within New York Oceanic FIR `KZWY`; - **Saint-Pierre et Miquelon** is an overseas collectivity of France located near Newfoundland, Canada, associated with letter `C` but airports use the `LF` prefix. However, other overseas territories use the local prefix: `T` in the Caribbean, `SO` for French Guyana, `NT` for Polynesia; - **Faroe islands** are an autonomous territory of Denmark: they are within Reykjavík FIR `BIRD` but Vágar airport is `EKVG` with `EK` for Denmark. Note that [Jan Mayen](https://en.wikipedia.org/wiki/Jan_Mayen) (Norway) also lies within Reykjavík FIR but this small volcanic uninhabited island has no airport; - **Falkland islands** (Malvinas) use both the `SF` (Stanley airport is `SFAL`) and the `EG` prefix of the United Kingdom (Mount Pleasant airport is `EGYP`); - **Côte d'Ivoire** use the `DI` prefix in spite of being part of the Dakar FIR `GOOO`; - **Macau** uses the `VM` prefix (Hong-Kong uses `VH`) but is covered by the Guangzhou FIR in **China region `Z`**; - **Antarctica** hosts many airfields (not listed here): some of them as labelled as `AT` followed by two digits (unrelated to `A` area for Melanesia), some keep the two digit code of the country which operates it, like `SC` for Chile, `EG` for the United Kingdom or `NZ` for New Zealand.35:T54c,plot_fir = function ( center_on, { fill, label_filters, scale_factor = 1, color = { scheme: "tableau10", legend: false }, flight_level = 100, caption = undefined } ) { const height = 0.6 * width; const centroid = d3.geoCentroid(center_on); const area = d3.geoArea(center_on); const scale = scale_factor * Math.log((2 * Math.PI) / area); const firs100 = firsAt(flight_level); return Plot.carto({ projection: d3 .geoOrthographic() .scale((scale * width) / 1.5 / Math.PI) .rotate(centroid.map((x) => -1 * x)) .translate([(0.7 * width) / 2, height / 2]), color: color, marks: [ Plot.feature({ type: "Sphere" }, { fill: "white" }), Plot.feature(graticule, { stroke: "#aaa", strokeWidth: 0.25 }), Plot.feature(land, { stroke: "#333", fill: "#ced4da" }), Plot.features(firs100, { fill, fillOpacity: 0.4, strokeWidth: 1.5, stroke: "#79706e" }), Plot.label(firs100.features.filter(label_filters), { fill: "#79706e", text: (d) => `${d.properties.designator}\n${d.properties.name}`, halo: true, fontSize: (14 * width) / 960 }) //Plot.feature({ type: "Sphere" }, { stroke: "black", strokeWidth: 2 }) ], width: 0.7 * width, height, caption }); }36:[{"id":"254a99fef9cfdc739794cf276a25ffce226b9d17d64789497bbed4935f1fda7d621149894d3a06e546f0e5c53beda2580db0166433ff2fac65397af1aa3627ea","href":"https://static.observableusercontent.com/files/254a99fef9cfdc739794cf276a25ffce226b9d17d64789497bbed4935f1fda7d621149894d3a06e546f0e5c53beda2580db0166433ff2fac65397af1aa3627ea","name":"countries-50m.json","type":"application/json","lastModified":1643495406097.552,"size":756420},{"id":"4e03f8625aa745ab949f0ff7d7420c19c6b79bb7973704b652c2b56b34726264971520523db4e8a94d5eea6e53339a8b00ff224e0b589f08182308e2ab3b464f","href":"https://static.observableusercontent.com/files/4e03f8625aa745ab949f0ff7d7420c19c6b79bb7973704b652c2b56b34726264971520523db4e8a94d5eea6e53339a8b00ff224e0b589f08182308e2ab3b464f","name":"airports.csv","type":"text/csv","lastModified":1643495472691.998,"size":449396},{"id":"f35567ec50da95d5b9fcbaddb3fc4d7a405a426c04a7888d086a6fc86fe92a0ba299571fbf57332c0689cc24a62ee1884cb637ef51883a1a9c0d0460d5beedec","href":"https://static.observableusercontent.com/files/f35567ec50da95d5b9fcbaddb3fc4d7a405a426c04a7888d086a6fc86fe92a0ba299571fbf57332c0689cc24a62ee1884cb637ef51883a1a9c0d0460d5beedec","name":"worldfirs.json","type":"application/json","lastModified":1643495449121.978,"size":315714}] 2f:{"title":"Flight Information Regions","cells":[{"id":1204,"value":"# Flight Information Regions","pinned":false,"hidden":false,"mode":"md"},{"id":1178,"value":"$31","pinned":false,"hidden":false,"mode":"ojs"},{"id":2825,"value":"toc(\"h2\")","pinned":false,"hidden":false,"mode":"ojs"},{"id":0,"value":"## Introduction\n\n**Flight Information Regions (FIR)** are the largest regular division of airspace in use in the world today. In theory, every portion of the atmosphere belongs to a specific FIR. Smaller countries’ airspace is encompassed by a single FIR; larger countries’ airspace is subdivided into a number of regional FIRs. Some FIRs encompass the territorial airspace of several countries, e.g. in Oceania, West Africa or in the Caribbean sea. Oceanic airspace is divided into Oceanic Information Regions and delegated to a controlling authority bordering that region.\n\nThe division among authorities is done by international agreement through the **International Civil Aviation Organization (ICAO)**.\n\n### Acknowledgement\n\nMany thanks to [@fil](https://observablehq.com/@fil) for the shepherding and support with [Plot carto](https://observablehq.com/@fil/plot-carto-0-5).","pinned":false,"hidden":false,"mode":"md"},{"id":1336,"value":"## Upper Information Regions\n\nDepending on countries, the airspace structure may be different according to altitudes, usually expressed in **Flight Level** (FL). In some countries including France, the altitude split occurs at FL 195 which corresponds to 19,500 ft, but other countries pick different altitudes like FL 180 in the US.\n\nOn the following map, we see the French airspace is divided into 5 FIR, but above FL 195, there is only one division corresponding to the country.","pinned":false,"hidden":false,"mode":"md"},{"id":1874,"value":"$32","pinned":false,"hidden":false,"mode":"ojs"},{"id":1485,"value":"## ICAO codes\n\nEach airspace has a four letter designator called an ICAO code.\n","pinned":false,"hidden":false,"mode":"md"},{"id":2376,"value":"viewof searchFIR = {\n const firs = topojson.feature(worldfirs, worldfirs.objects.data);\n return Inputs.search(\n firs.features\n .map((elt) =>\n Object({\n ...elt.properties,\n upper: elt.properties.upper ? elt.properties.upper : \"Infinity\"\n })\n )\n .filter((elt) => elt.type !== \"NO_FIR\"),\n {\n placeholder: \"Search FIR or UIR\"\n }\n );\n}","pinned":false,"hidden":false,"mode":"ojs"},{"id":1481,"value":"Table(searchFIR, {\n sort: \"designator\",\n layout: \"auto\",\n width: { name: \"60%\" },\n format: { designator: (elt) => html`${elt}` }\n})","pinned":false,"hidden":false,"mode":"ojs"},{"id":1432,"value":"\nWe often see such four letter ICAO codes used for airports in an operational context, although the common commercial practice handles three letter IATA identifiers: in the US, the most famous airport in New York is arguably `JFK`/`KJFK`, Chicago O'Hare airport is `ORD`/`KORD` (stands for *Orchard Place*); in Europe, London Heathrow `LHR` is labelled as `EGLL`, and Charles de Gaulle `CDG` airport in Paris as `LFPG`, etc.\n","pinned":false,"hidden":false,"mode":"md"},{"id":1796,"value":"viewof searchAirports = {\n const extractCode = function (icao) {\n return [\"K\", \"Y\", \"Z\"].includes(icao[0]) ? icao[0] : icao.slice(0, 2);\n };\n return Inputs.search(airports, {\n placeholder: \"Search airport, country, IATA or ICAO code\"\n });\n}","pinned":false,"hidden":false,"mode":"ojs"},{"id":1788,"value":"viewof selectAirports = Table(searchAirports, {\n sort: \"code\",\n layout: \"auto\",\n width: { icao: \"50px\", iata: \"50px\", name: \"50%\" },\n format: {\n icao: (elt) => html`${elt}`,\n iata: (elt) => html`${elt}`\n },\n columns: [\"iata\", \"icao\", \"name\", \"country\"],\n header: { iata: \"IATA\", icao: \"ICAO\" }\n})","pinned":false,"hidden":false,"mode":"ojs"},{"id":1808,"value":"The most important to notice here is the structure of ICAO codes: for instance, all codes starting with a `K` refer to the United States, `C` to Canada.\n\nIn other parts of the world, **the first letter refers to the area** and the **two first letters to the country**: `E` stands for Northern Europe, `EG` for the United Kingdom; `L` stands for Southern Europe, `LF` for France. One exception is Kosovo which, due to lack of further available letters in the `L` set got `BK`.","pinned":false,"hidden":false,"mode":"md"},{"id":1627,"value":"viewof searchCountry = {\n const extractCode = function (icao) {\n return [\"K\", \"Y\", \"Z\"].includes(icao[0]) ? icao[0] : icao.slice(0, 2);\n };\n const countryCodes = tidy(\n airports,\n mutate({ code: (d) => extractCode(d.icao) }),\n groupBy(\"code\", [summarize({ total: count(\"country\") })]),\n map((elt) => elt.total.map((x) => Object({ ...x, code: elt.code })))\n ).reduce((acc, elt) => acc.concat(elt), []);\n return Inputs.search(countryCodes, {\n placeholder: \"Search country or ICAO code\"\n });\n}","pinned":false,"hidden":false,"mode":"ojs"},{"id":1630,"value":"viewof selectCountry = Table(searchCountry, {\n sort: \"code\",\n layout: \"auto\",\n width: { code: \"50px\", country: \"50%\" },\n format: { code: (elt) => html`${elt}` },\n columns: [\"code\", \"country\", \"n\"],\n header: { n: \"number of large or medium scale airports\" }\n})","pinned":false,"hidden":false,"mode":"ojs"},{"id":1661,"value":"The following globe displays these one letter areas and plots one dot per airport. According to the region, we can see that for historical (colonial) reasons, **some country codes do not match the prefix of the corresponding FIR**.","pinned":false,"hidden":false,"mode":"md"},{"id":1918,"value":"$33","pinned":false,"hidden":false,"mode":"ojs"},{"id":1679,"value":"$34","pinned":false,"hidden":false,"mode":"md"},{"id":1740,"value":"## No FIR areas\n\nThere are still (few) places on Earth where no aviation services can be provided by any authority.\n\n**In the Barents sea, this thin stripe east of Svalbard/Spitbergen archipelago** (Norway) has smells of Cold War. The marine border between Norway and Russia had long been contested (see [Disputed territories](https://observablehq.com/@xoolive/disputed-territories)). Discussion was initiated in the 1970s and concluded in 2010 when the marine border was finally settled, roughly in the middle of this orange area.\n\nIn spite of this agreement, the airspace above is [still uncontrolled](https://aviation.stackexchange.com/questions/12810/why-is-there-a-strip-of-uncontrolled-airspace-between-russia-and-norway). For long-haul commercial aircraft crossing the area, this corresponds to about 5 minutes under the responsibility of no local authority.","pinned":false,"hidden":false,"mode":"md"},{"id":1719,"value":"plot_fir(\n firsAt(100).features.filter((elt) => elt.properties.type === \"NO_FIR\")[0],\n {\n fill: (elt) => elt.properties.type,\n label_filters: (d) => [\"E\", \"U\", \"B\"].includes(d.properties.designator[0])\n }\n)","pinned":false,"hidden":false,"mode":"ojs"},{"id":1842,"value":"**Another area in the South Pacific remains uncontrolled**. Transoceanic traffic usually requires a close collaboration between countries operating the oceanic airspaces, e.g. Shannon (Ireland) and Gander (Canada) control centres.\n\nIn this particular situation in the South Pacific, many aircraft avoid that large area because of lack of services.","pinned":false,"hidden":false,"mode":"md"},{"id":2175,"value":"plot_fir(\n firsAt(100).features.filter((elt) => elt.properties.type === \"NO_FIR\")[1],\n {\n fill: (elt) => elt.properties.type,\n label_filters: (d) =>\n [\n \"MMFO\",\n \"MMFR\",\n \"MHCC\",\n \"SEFG\",\n \"SPIM\",\n \"SCFZ\",\n \"NTTT\",\n \"SCIZ\",\n \"SCEZ\",\n \"SCTZ\",\n \"SKED\",\n \"SKEC\",\n \"KZMA\"\n ].includes(d.properties.designator),\n scale_factor: 0.65\n }\n)","pinned":false,"hidden":false,"mode":"ojs"},{"id":2065,"value":"## Fun facts\n\n\n- The smallest FIR on Earth is in central Europe: **Ljubljana FIR** is in charge of Slovenia 🇸🇮 on a surface of roughly 20,000 square kilometers. \n The largest FIR is the **Oakland Oceanic FIR**: it spans over almost all the Northern Pacific Ocean, for roughly 50,000,000 square kilometers.","pinned":false,"hidden":false,"mode":"md"},{"id":2081,"value":"{\n const minAreaFIR = d3.least(firsAt(180).features, d3.geoArea);\n const minPlot = plot_fir(minAreaFIR, {\n fill: (elt) =>\n elt.properties.designator === minAreaFIR.properties.designator,\n label_filters: (elt) => [\"E\", \"L\"].includes(elt.properties.designator[0]),\n scale_factor: 2.5,\n caption: \"Smallest area FIR\"\n });\n const maxAreaFIR = d3.greatest(firsAt(180).features, d3.geoArea);\n const maxPlot = plot_fir(maxAreaFIR, {\n fill: (elt) =>\n elt.properties.designator === maxAreaFIR.properties.designator,\n label_filters: (elt) =>\n [\n \"KZAK\",\n \"RJJJ\",\n \"RPHI\",\n \"AYPM\",\n \"AGGG\",\n \"ANAU\",\n \"NFFF\",\n \"NTTT\",\n \"YBBB\",\n \"PAZA\",\n \"KZSE\",\n \"KZOA\",\n \"MMFO\",\n \"MMFR\",\n \"NZZO\",\n \"NZZC\"\n ].includes(elt.properties.designator),\n caption: \"Largest area FIR\"\n });\n return html`

${minPlot} ${maxPlot}`;\n}","pinned":false,"hidden":false,"mode":"ojs"},{"id":2670,"value":"### Exclaves and enclaves","pinned":false,"hidden":false,"mode":"md"},{"id":2302,"value":"There are two FIR areas which are exclaved out of their letter area:\n- **Kaliningrad** is a Russian exclave on the Baltic sea: `UMKK` is naturally surrounded by `E` letter FIR areas;","pinned":false,"hidden":false,"mode":"md"},{"id":2421,"value":"{\n const UMKK = firsAt(180).features.filter(\n (elt) => elt.properties.designator == \"UMKK\"\n )[0];\n return plot_fir(UMKK, {\n fill: (elt) => elt.properties.designator[0],\n label_filters: (elt) => true,\n scale_factor: 1.3,\n color: { range: colorscale },\n caption: \"Kaliningrad FIR is exclaved in the E (Northern Europe) area\"\n });\n}","pinned":false,"hidden":false,"mode":"ojs"},{"id":2677,"value":"- **Hong-Kong** goes as `VH`, **Macau** as `VM`, **Taiwan** as `RC`, and **mainland China** with letter `Z`, together with Mongolia and North Korea. However, Macau `VM` is covered by the Guangzhou FIR `ZGZU`, because it could have been simpler.","pinned":false,"hidden":false,"mode":"md"},{"id":2319,"value":"{\n const VHHK = firsAt(180).features.filter(\n (elt) => elt.properties.designator == \"VHHK\"\n )[0];\n return plot_fir(VHHK, {\n fill: (elt) => elt.properties.designator[0],\n label_filters: (elt) => true,\n color: { range: colorscale },\n caption: \"Hong-Kong FIR is exclaved in the Z (China) area\"\n });\n}","pinned":false,"hidden":false,"mode":"ojs"},{"id":2465,"value":"- Roberts FIR covers the airspace for **Guinea Conakry, Liberia and Sierra Leone**. It is fully enclaved in the Dakar FIR.\n","pinned":false,"hidden":false,"mode":"md"},{"id":2684,"value":"{\n const GLRB = firsAt(100).features.filter(\n (elt) => elt.properties.designator == \"GLRB\"\n )[0];\n return plot_fir(GLRB, {\n fill: (elt) => elt.properties.designator === \"GOOO\",\n label_filters: (elt) => true,\n scale_factor: 0.8,\n color: { scheme: \"tableau10\" }\n });\n}","pinned":false,"hidden":false,"mode":"ojs"},{"id":2723,"value":"Baku FIR is the only FIR consisting of two disconnected components, the **Nakhchivan Autonomous Republic** being an exclave of Azerbaijan.","pinned":false,"hidden":false,"mode":"md"},{"id":2729,"value":"{\n const UBBA = firsAt(100).features.filter(\n (elt) => elt.properties.designator == \"UBBA\"\n )[0];\n return plot_fir(UBBA, {\n fill: (elt) => elt.properties.designator === \"UBBA\",\n label_filters: (elt) => true,\n scale_factor: 2.5,\n color: { scheme: \"tableau10\" }\n });\n}","pinned":false,"hidden":false,"mode":"ojs"},{"id":2043,"value":"### Appendix","pinned":false,"hidden":false,"mode":"md"},{"id":2668,"value":"letter_areas.filter(\n (elt) => elt.type === \"MultiPolygon\" && elt.coordinates.length > 1\n)","pinned":false,"hidden":false,"mode":"ojs"},{"id":2077,"value":"$35","pinned":false,"hidden":false,"mode":"ojs"},{"id":2605,"value":"colorscale = [\n \"#393b79\",\n \"#5254a3\",\n \"#6b6ecf\",\n \"#9c9ede\",\n \"#637939\",\n \"#8ca252\",\n \"#b5cf6b\",\n \"#cedb9c\",\n \"#8c6d31\",\n \"#bd9e39\",\n \"#e7ba52\",\n \"#e7cb94\",\n \"#843c39\",\n \"#ad494a\",\n \"#d6616b\",\n \"#e7969c\",\n \"#7b4173\",\n \"#a55194\",\n \"#ce6dbd\",\n \"#de9ed6\",\n \"#636363\",\n \"#969696\",\n \"#bdbdbd\",\n \"#d9d9d9\"\n]","pinned":false,"hidden":false,"mode":"ojs"},{"id":699,"value":"letter_areas = {\n const letters = new Set(\n firsAt(100)\n .features.filter((elt) => elt.properties.designator)\n .map((elt) => elt.properties.designator[0])\n );\n const areas = Array(...letters).map((letter) =>\n Object({\n ...d3.geoStitch(\n topojson.merge(\n worldfirs,\n worldfirs.objects.data.geometries\n .filter((elt) => elt.properties.designator)\n .filter(\n (d) =>\n d.properties.lower <= 100 &&\n 100 < (d.properties.upper ? d.properties.upper : 999)\n )\n .filter((elt) => elt.properties.designator[0] === letter)\n )\n ),\n properties: { designator: letter }\n })\n );\n return areas;\n}","pinned":false,"hidden":false,"mode":"ojs"},{"id":2632,"value":"letter_centroids = {\n const letters = new Set(\n firsAt(100)\n .features.filter((elt) => elt.properties.designator)\n .map((elt) => elt.properties.designator[0])\n );\n return Array(...letters)\n .filter((letter) => letter !== undefined)\n .map((letter) =>\n Object({\n letter: letter,\n latlon: d3.geoCentroid(\n Object({\n type: \"MultiPoint\",\n coordinates: firsAt(100)\n .features.filter((d) => d.properties.designator[0] === letter)\n .map((elt) => d3.geoCentroid(elt.geometry))\n })\n )\n })\n );\n}","pinned":false,"hidden":false,"mode":"ojs"},{"id":22,"value":"outline = ({type: \"Sphere\"})","pinned":false,"hidden":false,"mode":"ojs"},{"id":114,"value":"graticule = d3.geoGraticule10()","pinned":false,"hidden":false,"mode":"ojs"},{"id":16,"value":"land = topojson.feature(world, world.objects.land)","pinned":false,"hidden":false,"mode":"ojs"},{"id":1241,"value":"countries = topojson.feature(world, world.objects.countries)","pinned":false,"hidden":false,"mode":"ojs"},{"id":105,"value":"borders = topojson.mesh(world, world.objects.countries, (a, b) => a !== b)","pinned":false,"hidden":false,"mode":"ojs"},{"id":13,"value":"world = FileAttachment(\"countries-50m.json\").json()","pinned":false,"hidden":false,"mode":"ojs"},{"id":1011,"value":"airports = FileAttachment(\"airports.csv\").csv({ typed: true })","pinned":false,"hidden":false,"mode":"ojs"},{"id":125,"value":"worldfirs = FileAttachment(\"worldfirs.json\").json()","pinned":false,"hidden":false,"mode":"ojs"},{"id":1185,"value":"firsAt = function (fl) {\n /* This function picks all the FIR at a given flight level */\n const firs = topojson.feature(worldfirs, worldfirs.objects.data);\n const fixStitch = function (geometry) {\n const a = d3.geoStitch(geometry);\n a.type = \"Polygon\";\n a.coordinates = a.coordinates.flat();\n return a;\n };\n firs.features = firs.features\n .filter(\n (elt) =>\n elt.properties.lower <= fl &&\n fl < (elt.properties.upper ? elt.properties.upper : 999)\n )\n .map((elt) =>\n Object({\n type: \"Feature\",\n properties: {\n ...elt.properties,\n // add an empty string if the designator is empty (NO_FIR areas)\n designator: elt.properties.designator ? elt.properties.designator : \"\"\n },\n // Fix that bug for geoStitch\n geometry:\n elt.properties.designator === \"NZZO\"\n ? fixStitch(elt.geometry)\n : d3.geoStitch(elt.geometry)\n })\n );\n return firs;\n}","pinned":false,"hidden":false,"mode":"ojs"},{"id":1968,"value":"import { tidy, groupBy, mutate, summarize, count, map } from \"@pbeshai/tidyjs\"","pinned":false,"hidden":false,"mode":"ojs"},{"id":2809,"value":"import { toc } from \"@nebrius/indented-toc\"","pinned":false,"hidden":false,"mode":"ojs"},{"id":1964,"value":"import { Table } from \"@observablehq/inputs\"","pinned":false,"hidden":false,"mode":"ojs"},{"id":2400,"value":"import {addTooltips} from \"@mkfreeman/plot-tooltip\"","pinned":false,"hidden":false,"mode":"ojs"},{"id":573,"value":"// Plot.carto is an experimental plugin for Observable Plot\nimport { Plot } from \"@fil/plot-carto-0-5\"","pinned":false,"hidden":false,"mode":"ojs"},{"id":161,"value":"d3 = require(\"d3@6\", \"d3-geo@3\", \"d3-geo-projection@4\", \"d3-geo-polygon@1\", \"d3-selection@1\", \"d3-fetch@1\", \"d3-inertia@0.4\")","pinned":false,"hidden":false,"mode":"ojs"},{"id":546,"value":"topojson = require(\"topojson-client@3\", \"topojson-server@3\", \"topojson-simplify@3\")","pinned":false,"hidden":false,"mode":"ojs"}],"files":"$W36","stdlib":"1","titling":"auto"}