2c:null 2d:["$","title",null,{"children":"Générateur de méridiens et parallèles | Atelier de cartographie de Sciences Po | Observable"}] 32:T739,33:[{"id":"c9329ccddcb2fc3bf6daf7d6fed1d4c8cabbe2c09f73a5984ab5c1f968f1470f59935e90c4c07216568d3c10c3f539d21ec1c56ed29d5477230a6b6ce847d4c9","href":"https://static.observableusercontent.com/files/c9329ccddcb2fc3bf6daf7d6fed1d4c8cabbe2c09f73a5984ab5c1f968f1470f59935e90c4c07216568d3c10c3f539d21ec1c56ed29d5477230a6b6ce847d4c9","name":"urban_500k.json","type":"application/json","lastModified":1651668864697.03,"size":280167},{"id":"2fac8ff4da691832a98924ce984312947207d4ab35a785d68ff10ac4e254fa956aa298b1f48b6d885552190b63b0eb91a211d785942e35e250e0f4b1415bb3b4","href":"https://static.observableusercontent.com/files/2fac8ff4da691832a98924ce984312947207d4ab35a785d68ff10ac4e254fa956aa298b1f48b6d885552190b63b0eb91a211d785942e35e250e0f4b1415bb3b4","name":"countries_110m.topojson","type":"application/octet-stream","lastModified":1651668868049.025,"size":90062}] 30:{"id":"86b55afdaf5f6aa6","slug":"generateur-de-meridiens-et-paralleles","title":"Générateur de méridiens et parallèles","thumbnail":"6985e52c985e5a8e86e3840314ad759f0ad0d09c0d4eba31e84cb59bfd376cf8","access_level":"public","create_time":"$D2022-05-04T12:49:27.942Z","update_time":"$D2023-03-02T11:01:34.345Z","view_time":null,"first_public_time":"$D2022-06-07T09:42:13.064Z","fork":false,"stars":6,"starred":false,"owner":{"type":"team","id":"5d76df5eab7f8bb7","login":"ateliercartographie","name":"Atelier de cartographie de Sciences Po","avatar_url":"https://avatars-next.observableusercontent.com/fab2304a50866da3a682fdbbdf200ecb01ddfd5fbf74f60756d36188cfd2cf68","tier":"starter_2024"},"version":122,"publish_version":null,"role":null,"authored":false,"authors":[{"type":"individual","id":"b5f87f2a35829281","login":"tombor","name":"Thomas Ansart","avatar_url":"https://avatars-next.observableusercontent.com/b086dcc95470aae08b776435f7604190c606884a2187354d54b5fbae116aa241","tier":null}],"members":[{"type":"team","id":"5d76df5eab7f8bb7","login":"ateliercartographie","name":"Atelier de cartographie de Sciences Po","avatar_url":"https://avatars-next.observableusercontent.com/fab2304a50866da3a682fdbbdf200ecb01ddfd5fbf74f60756d36188cfd2cf68","tier":"starter_2024","role":"editor"},{"type":"individual","id":"b5f87f2a35829281","login":"tombor","name":"Thomas Ansart","avatar_url":"https://avatars-next.observableusercontent.com/b086dcc95470aae08b776435f7604190c606884a2187354d54b5fbae116aa241","tier":null,"role":"editor"}],"comments":[],"custom_thumbnail":false,"trashed":false,"lapsed":null,"subscribed":null,"forks":1,"collection":{"id":"ae5edacf60f09e75","slug":"graticule","title":"Graticule","owner":{"id":"5d76df5eab7f8bb7","login":"ateliercartographie","name":"Atelier de cartographie de Sciences Po"}},"type":"notebook","body":{"title":"Générateur de méridiens et parallèles","cells":[{"id":0,"value":"# Générateur de méridiens et parallèles\n## Renvoyer une ligne au format geojson, à partir d'une valeur de latitude ou de longitude\n> Ce générateur est utilisé dans [**Graticule**](https://www.sciencespo.fr/cartographie/graticule/), un outil conçu et développé par l’Atelier de cartographie de Sciences Po. Gratuit et open source, il permet à tout type de public de s’initier à la cartographie et ses concepts par la réalisation de fond de carte.","pinned":false,"hidden":false,"mode":"md","author":"$undefined","summary":"$undefined","output":"","database":"$undefined"},{"id":88,"value":"## Construction de la fonction\n\nLa fonction comprend 4 arguments :\n+ `value` => la valeur en degré de la ligne à générer. Par défaut `0`\n+ `direction` => au choix latitude, lat ou longitude, lon. Par défaut `\"lat\"`\n+ `precision` => écart en degré entre chaque couple de coordonnées de la ligne générée. Par défaut `2.5`\n+ `geojson` => si `true` renvoie la ligne au format geojson (de type [`LineString`](https://datatracker.ietf.org/doc/html/rfc7946#section-3.1.4)), si `false` renvoie les coordonnées au format array. Par défaut `false`","pinned":false,"hidden":false,"mode":"md","author":"$undefined","summary":"$undefined","output":"","database":"$undefined"},{"id":9,"value":"geoLine = (value = 0, direction = 'lat', precision = 2.5, geojson = false) => {\n const v = parseFloat(value)\n precision = parseFloat(precision)\n const lineString = {type: \"LineString\", coordinates: []}\n let coordinates\n \n switch (direction) {\n \n case 'latitude':\n case 'lat':\n coordinates = d3.range(-180, 180+1, precision).map(x => [x,v])\n return geojson ? (lineString.coordinates = coordinates, lineString) : coordinates\n break\n \n case 'longitude':\n case 'long':\n case 'lon':\n coordinates = d3.range(-90, 90+1, precision).map(y => [v,y])\n return geojson ? (lineString.coordinates = coordinates, lineString) : coordinates\n break\n \n default:\n return `'${direction}' n'est pas une valeur de direction possible. 'lat' ou 'long' attendu`\n }\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":10,"value":"## Importance de la précision\nLa précision détermine l'espace entre chaque couple de coordonnées. Plus la précision est grande plus la distance entre deux points de la ligne augmente. Dans le contexte de méridiens et de parallèles, qui peuvent être représentés selon une variété de projection cartographique, la précision a des effets visibles.\n\nVoir par exemple le cas du tropique du Cancer selon deux projections : équirectangulaire et Lambert azimutale équivalente. \n\n_Cliquer sur \"Play\" pour augmenter la précision du tracé_","pinned":false,"hidden":false,"mode":"md","author":"$undefined","summary":"$undefined","output":"","database":"$undefined"},{"id":15,"value":"viewof step = Scrubber(d3.range(4, 90+1, 2).reverse(), {autoplay: false, loop: false, alternate: true})","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":18,"value":"{\n const projA = d3.geoEquirectangular()\n const pathA = d3.geoPath(projA)\n d3.geoPath(projA.fitWidth(width, outline)).bounds(outline)\n\n const projB = d3.geoAzimuthalEqualArea()\n const pathB = d3.geoPath(projB)\n d3.geoPath(projB.fitWidth(width, outline))\n\n const cancer = geoLine(23.436, 'lat', step, true)\n const dots = { type: \"MultiPoint\", coordinates: geoLine(23.436, 'lat', step) }\n \n return htl.html`\n\n`\n}","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":20,"value":"## Test de la fonction","pinned":false,"hidden":false,"mode":"md","author":"$undefined","summary":"$undefined","output":"","database":"$undefined"},{"id":24,"value":"// Latitude 10° au format array\ngeoLine(10, 'lat', 2.5, false)","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":25,"value":"// Latitude 10° au format array\n// en prenant en compte les valeurs par défaut \ngeoLine(10)","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":27,"value":"// Latitude 10° au format geojson\ngeoLine(10, 'lat', 2.5, true)","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":29,"value":"// Longitude -70° au format array\n// précision de 30° = chaque couple de coordonnées est espacé de 30° de latitude\ngeoLine(-60, 'lon', 30)","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":31,"value":"// Longitude -70° au format geojson\ngeoLine(-60, 'lon', 30, true)","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":33,"value":"## Le cas de Graticule\nPour les besoins de [l'outil](https://www.sciencespo.fr/cartographie/graticule/), 7 lignes remarquables ont été sélectionnées :\n+ Cercle polaire arctique _(66.563° de latitude)_\n+ Tropique du Cancer _(23.436° de latitude)_\n+ Équateur _(0° de latitude)_\n+ Tropique du Capricorne _(-23.436° de latitude)_\n+ Cercle polaire antarctique _(-66.563° de latitude)_\n+ Méridien de Greenwitch _(0° de longitude)_\n+ Antiméridien _(180° de longitude)_\n\nCes 7 lignes sont générées et rassemblées dans l'objet `geographicLines` ci-dessous au sein d'un geojson de type `MultiLineString`","pinned":false,"hidden":false,"mode":"md","author":"$undefined","summary":"$undefined","output":"","database":"$undefined"},{"id":38,"value":"geographicLines = ({\n type: \"MultiLineString\",\n coordinates: [\n geoLine(66.563, 'lat'), // Cercle polaire arctique\n geoLine(23.436, 'lat'), // Tropique du Cancer\n geoLine(0, 'lat', 90), // Équateur\n geoLine(-23.436, 'lat'), // Tropique du Capricorne\n geoLine(-66.563, 'lat'), // Cercle polaire antarctique\n geoLine(0, 'lon', 90), // Méridien de Greenwitch\n geoLine(180, 'lon', 90), // Antiméridien\n ]\n})","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":93,"value":"**Affichage des 7 lignes avec une projection orthographique.**\n\n_Cliquer sur \"Play\" pour faire tourner le globe_","pinned":false,"hidden":false,"mode":"md","author":"$undefined","summary":"$undefined","output":"","database":"$undefined"},{"id":39,"value":"viewof rotate = Scrubber(d3.range(-360, 360+1,1), {autoplay: false, loop: false, alternate: false})","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":41,"value":"$32","pinned":false,"hidden":false,"mode":"html","author":"$undefined","summary":"$undefined","output":"","database":"$undefined"},{"id":48,"value":"---\n## Paramètres de la carte","pinned":false,"hidden":false,"mode":"md","author":"$undefined","summary":"$undefined","output":"","database":"$undefined"},{"id":51,"value":"projection = d3.geoOrthographic().rotate([rotate,rotate])","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":52,"value":"path = d3.geoPath(projection)","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":54,"value":"height = {\n const [[x0, y0], [x1, y1]] = d3.geoPath(projection.fitWidth(width, outline)).bounds(outline);\n const dy = Math.ceil(y1 - y0)\n return dy;\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":56,"value":"outline = ({type: \"Sphere\"})","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":58,"value":"Fond des pays d'après le carnet [Adapter Natural Earth : les pays](https://observablehq.com/d/6671f98c17dc8802)","pinned":false,"hidden":false,"mode":"md","author":"$undefined","summary":"$undefined","output":"","database":"$undefined"},{"id":107,"value":"import {countries_simplified} from \"@tombor/adapter-natural-earth-les-pays\"","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":63,"value":"// conversion de topojson en geojson\ncountries_110m = topojson.feature(countries_simplified, countries_simplified.objects.countries_110m)","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":67,"value":"Zones urbaines denses de plus de 500 000 habitants d'après le [Global Human Settlement](https://ghsl.jrc.ec.europa.eu/index.php) (Commission européenne, JRC)","pinned":false,"hidden":false,"mode":"md","author":"$undefined","summary":"$undefined","output":"","database":"$undefined"},{"id":69,"value":"urban = {\n const geo = await FileAttachment(\"urban_500k.json\").json()\n return topojson.feature(geo, geo.objects.urban)\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":73,"value":"---\n## Librairies","pinned":false,"hidden":false,"mode":"md","author":"$undefined","summary":"$undefined","output":"","database":"$undefined"},{"id":76,"value":"","pinned":false,"hidden":false,"mode":"html","author":"$undefined","summary":"$undefined","output":"","database":"$undefined"},{"id":82,"value":"import {Scrubber} from \"@mbostock/scrubber\"","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"}],"files":"$W33","stdlib":"1","titling":"auto"}} 31:"$30:body"