41:null 42:["$","title",null,{"children":"Dec Time Zones | Decalendar | Observable"}] 48:T598,The map below shows how Dec divides the world up with 10 [lines of longitude](https://en.wikipedia.org/wiki/Meridian_%28geography%29#:~:text=the%20locus%20connecting%20points%20of%20equal%20longitude), each spaced 1 deciturn (10% of a turn) apart. Dec is a [measurement system](https://en.wikipedia.org/wiki/System_of_units_of_measurement#:~:text=a%20collection%20of%20units%20of%20measurement%20and%20rules%20relating%20them%20to%20each%20other) that [I](https://maptv.github.io) created to measure⏳time,📍position,🧭orientation,📐angles, and🔄cycles in [turns](https://en.wikipedia.org/wiki/Turn_%28angle%29#:~:text=a%20unit%20of%20plane%20angle%20measurement%20equal%20to%202%CF%80%C2%A0radians%2C%20360%C2%A0degrees) ([${tex`\tau`}](https://en.wikipedia.org/wiki/Turn_%28angle%29#:~:text=the%20Greek%20letter,to%20one%20turn)) instead of months, weeks, hours, minutes, seconds, and degrees. For time measurement, Dec uses days and years, which are turns of a [celestial body](https://en.wikipedia.org/wiki/Astronomical_object#:~:text=a%20single%2C%20tightly%20bound%2C%20contiguous%20entity) on [its axis](https://en.wikipedia.org/wiki/Axial_tilt#:~:text=the%20imaginary%20line%20that%20passes%20through%20both%20the%20north%20pole%20and%20south%20pole) and around [the point it orbits](https://en.wikipedia.org/wiki/Barycenter_%28astronomy%29#:~:text=the%20point%20about%20which%20the%20bodies%20orbit), respectively.49:T5bb,The map above shows how [Longitude 0](https://en.wikipedia.org/wiki/126th_meridian_west#:~:text=a%20line%20of%20longitude%20that%20extends%20from%20the%20North%20Pole%20across%20the%20Arctic%20Ocean%2C%20North%20America%2C%20the%20Pacific%20Ocean%2C%20the%20Southern%20Ocean%2C%20and%20Antarctica%20to%20the%20South%20Pole), the Dec [International Date Line](https://en.wikipedia.org/wiki/International_Date_Line#:~:text=the%20line%20between%20the%20South%20and%20North%20Poles%20that%20is%20the%20boundary%20between%20one%20calendar%20day%20and%20the%20next) and [prime meridian](https://en.wikipedia.org/wiki/Prime_meridian#:~:text=an%20arbitrarily%2Dchosen%20meridian%20%28a%20line%20of%20longitude%29%20in%20a%20geographic%20coordinate%20system%20at%20which%20longitude%20is%20defined%20to%20be%200%C2%B0), cuts across the Atlantic Ocean just West of Africa and marks the start of Zone 0, the leftmost Dec time zone on the map. Dec has 10 time zones which are each 1 deciturn (10% of a turn) wide and are numbered 0 through 9, like the [lines of longitude](https://en.wikipedia.org/wiki/Meridian_%28geography%29#:~:text=words%2C%20it%20is-,a%20line%20of%20longitude,-.%20The%20position%20of) that separate them. For more Dec maps, check out these notebooks: - [Decalendar](/@dec/al) - [Decalc](/@dec/alc) - [Decaliper](/@dec/ali) - [Declock](/@dec/loc) - [Solar terminator](/@dec/solar-terminator) - [The Sun's view of the Earth](/@dec/the-suns-view-of-the-earth)4a:T5bb,// https://observablehq.com/@bayre/svg-swatches function swatches({ colour, swatchRadius = 7.5, swatchPadding = swatchRadius * (2/3), labelFont = "12px sans-serif", labelFormat = x => x, labelPadding = swatchRadius * 1.5, marginLeft = 0 } = {}) { const spacing = colour .domain() .map(d => labelFormat(d)) .map(d => getLabelLength(d, labelFont) + (swatchRadius * 2) + swatchPadding + labelPadding) .map((_, i, g) => d3.cumsum(g)[i] + marginLeft) const width = d3.max(spacing) const height = swatchRadius * 6 + swatchPadding * 6 const svg = d3.create("svg") .attr("id", "swatches") .attr("width", width) .attr("height", height) .attr("viewBox", [0, 0, width, height]) .style("margin-top", "-28px") .style("overflow", "visible") .style("display", "block"); const g = svg .append("g") .attr("transform", `translate(0, ${height / 2})`) .selectAll("g") .data(colour.domain()) .join("g") .attr("transform", (d, i) => `translate(${spacing[i - 1] || marginLeft}, 0)`); g.append("circle") .attr("fill", colour) .attr("stroke", "black") .attr("r", swatchRadius) .attr("cx", swatchRadius) .attr("cy", 0); g.append("text") .attr("x", swatchRadius * 2 + swatchPadding) .attr("y", 0) .attr("dominant-baseline", "central") .style("font", labelFont) .text(d => labelFormat(d)); return svg.node() 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Zones","thumbnail":"eae218d3214815ce0f568dceb36a32e644a90fe239d768efd25f87a50a262c93","access_level":"public","create_time":"$D2025-03-16T06:30:48.941Z","update_time":"$D2025-04-23T17:20:14.570Z","view_time":null,"first_public_time":"$D2025-03-16T07:40:31.532Z","has_unpublished_edits":null,"fork":{"id":"df60fbc8a63a74c4","slug":"time-zones","title":"Time Zones","owner":{"id":"8c2e47252fd4995c","login":"mbostock","name":"Mike Bostock"}},"stars":0,"starred":false,"owner":{"type":"team","id":"4d2c79bb5e10ae73","login":"dec","name":"Decalendar","avatar_url":"https://avatars-next.observableusercontent.com/3c5aab661f4412ebb09266240b4c149ecdc2623ea7af89b8a12d28de877dcd08","tier":"starter_2024","bio":"","following":false},"version":337,"publish_version":null,"role":null,"authored":false,"authors":[{"type":"individual","id":"cad5899c8da00e88","login":"maptv","name":"Martin 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Earth](https://gist.github.com/mbostock/f0ae25cf1f057d443ca903277e3eb330)`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":285,"value":"$48","pinned":false,"hidden":false,"mode":"md","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"","database":"$undefined"},{"id":253,"value":"swatches({\n colour: d3.scaleOrdinal([...Array(10).keys()], hsla10)\n})","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":16,"value":"map = 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[\n `hsla(0, ${s / 10}%, ${l / 10}%, ${a / 10}%)`, // red\n // `hsla(340, ${s / 10}%, ${l / 10}%, ${a / 10}%)`, // magentared\n `hsla(300, ${s / 10}%, ${l / 10}%, ${a / 10}%)`, // magenta\n `hsla(280, ${s / 10}%, ${l / 10}%, ${a / 10}%)`, // violet\n `hsla(240, ${s / 10}%, ${l / 10}%, ${a / 10}%)`, // blue\n `hsla(200, ${s / 10}%, ${l / 10}%, ${a / 10}%)`, // azure\n `hsla(180, ${s / 10}%, ${l / 10}%, ${a / 10}%)`, // cyan\n // `hsla(160, ${s / 10}%, ${l / 10}%, ${a / 10}%)`, // cyangreen\n `hsla(120, ${s / 10}%, ${l / 10}%, ${a / 10}%)`, // green\n `hsla(80, ${s / 10}%, ${l / 10}%, ${a / 10}%)`, // lime\n `hsla(60, ${s / 10}%, ${l / 10}%, ${a / 10}%)`, // yellow\n `hsla(40, ${s / 10}%, ${l / 10}%, ${a / 10}%)`, // orange\n `hsla(0, ${s / 10}%, ${l / 10}%, ${a / 10}%)`, // red\n]","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":195,"value":"coor = [[[-18, -90], [-18, 90], [18, 90], [18, -90], [-18, -90], ]]","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":197,"value":"deczones = [...Array(10).keys()].map(\n i => ({\n \"type\": \"Feature\",\n \"geometry\": {\n \"type\": \"Polygon\",\n \"coordinates\": [coor[0].map(t => [t[0]+36*i, t[1]])]},\n \"properties\": []\n})\n)","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":20,"value":"projection = 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l).precision(0.2);\n return dy;\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":25,"value":"outline = ({type: \"Sphere\"})","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":28,"value":"graticule = d3.geoGraticule().stepMinor([15, 10])()","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":8,"value":"timezones = 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