2d:null 2e:["$","title",null,{"children":"Introduction to leaflet and D3 | lilpeasant | Observable"}] 33:T586,map = { // You'll often see Leaflet examples initializing a map like L.map('map'), // which tells the library to look for a div with the id 'map' on the page. // In Observable, we instead create a div from scratch in this cell (called "map") let container = DOM.element('div', { style: `width:${width}px;height:${width/1.6}px` }); // This component utilizes "yield" which pauses the execution of this code block // returns the value of container back to the notebook which allows the // div to be placed on the page. This is important, because Leaflet uses // the div's .offsetWidth and .offsetHeight (used to get current size of the div) // to size the map. If I were to only return the container at the end of this method, // Leaflet might get the wrong idea about the map's size. yield container; // Now we create a map object and add a layer to it. let map = L.map(container).setView([49.2527, -123.1207], 11.5); // initializes the map, sets zoom & coordinates let osmLayer = L.tileLayer('https://{s}.tile.openstreetmap.org/{z}/{x}/{y}.png', { attribution: '© OpenStreetMap contributors' }).addTo(map); //This adds the tile layer to the map. The map dynamically loads tiles based on current view the experience smooth and seamless. Make sure to add attribution to your map. osm = open street map. L = layer }34:T5b8, Dots = { const width = 600; const height = 400; const svg = d3.select(DOM.svg(width, height)) const projection = d3.geoMercator().fitExtent([[50,50], [width-50, height-50]], Wcities); const points = svg.selectAll('circle') .data(Wcities.features) .join('circle') .attr('fill', 'blue') .attr('cx', d => projection(d.geometry.coordinates)[0]) .attr('cy', d => projection(d.geometry.coordinates)[1]) .attr('r', 10) .on('mouseover', function() { d3.select(this).transition() .duration('150') .attr('fill', 'red') .attr('r', '15') }) .on('mouseout', function() { d3.select(this).transition() .duration('300') .attr('fill', 'blue') .attr('r', '10') }) const text = svg.selectAll('text') .data(Wcities.features) .join('text') .attr('font-size','9') .attr('x', d => projection(d.geometry.coordinates)[0]+15) .attr('y', d => projection(d.geometry.coordinates)[1]+3) .text(d => d.properties.Name) return svg.node() }35:T631,D3VanAreasMap = { let container = DOM.element('div', { style: `width:${width}px;height:${width/1.6}px` }); yield container; let map = L.map(container).setView([49.2527, -123.1207], 11.5); let osmLayer = L.tileLayer('https://{s}.tile.openstreetmap.org/{z}/{x}/{y}.png', { attribution: '© OpenStreetMap contributors' }).addTo(map); //initialize svg to add to map L.svg().addTo(map) //Create selection using D3 const overlay = d3.select(map.getPanes().overlayPane) const svg = overlay.select('svg') // create a group that is hidden during zooming const g = svg.append('g').attr('class', 'leaflet-zoom-hide') // Use Leaflets projection API for drawing svg path (creates a stream of projected points) const projectPoint = function(x, y) { const point = map.latLngToLayerPoint(new L.LatLng(y, x)) this.stream.point(point.x, point.y) } // Use d3's custom geo transform method to implement the above const projection = d3.geoTransform({point: projectPoint}) // creates geopath from projected points (SVG) const pathCreator = d3.geoPath().projection(projection) const areaPaths = g.selectAll('path') .data(VanAreas.features) .enter() .append('path') .attr('fill-opacity', 0.3) .attr('stroke', 'black') .attr('stroke-width', 2.5) // Function to place svg based on zoom const onZoom = () => areaPaths.attr('d', pathCreator) // initialize positioning onZoom() // reset whenever map is moved map.on('zoomend', onZoom) }36:[{"id":"50886802bef6525bb0c59e392b3744a58d6b11da68399a2738366370d9924ed41c1017d9c1c2358798c1327ea891c22545fd5be224cdf1961e3c4f36d33ac950","href":"https://static.observableusercontent.com/files/50886802bef6525bb0c59e392b3744a58d6b11da68399a2738366370d9924ed41c1017d9c1c2358798c1327ea891c22545fd5be224cdf1961e3c4f36d33ac950","name":"map.geojson","type":"application/geo+json","lastModified":1573842813876.119,"size":980},{"id":"e8a1c62e61765cd84ab67631082775bd53395bcd4f1a6d6fd19f74e236194b9e9606ab4b04114ed5024d04dfffa5a7e1685f0cdf4707636dc571a8e6eef584a8","href":"https://static.observableusercontent.com/files/e8a1c62e61765cd84ab67631082775bd53395bcd4f1a6d6fd19f74e236194b9e9606ab4b04114ed5024d04dfffa5a7e1685f0cdf4707636dc571a8e6eef584a8","name":"VancouverAreaSize.json","type":"application/json","lastModified":1573842813876.119,"size":52857},{"id":"8ef4099dcffc981f20c5cc8429be6f7d1c8bd99039aab8730a7e279e57af0896388ff67f9f1b3eaed9db97efc61545464292d53108541ea6af231b5531328bd4","href":"https://static.observableusercontent.com/files/8ef4099dcffc981f20c5cc8429be6f7d1c8bd99039aab8730a7e279e57af0896388ff67f9f1b3eaed9db97efc61545464292d53108541ea6af231b5531328bd4","name":"feds.json","type":"application/json","lastModified":1573842813876.119,"size":880675},{"id":"ec39637aea3af5a797d7e4a6354ff295953050798729fe934a0d542b8ff7d89e6e98b5e43db9c6a33dd2a21a19a20e1b9ce61b98880bba9b126a740cf0eddc6e","href":"https://static.observableusercontent.com/files/ec39637aea3af5a797d7e4a6354ff295953050798729fe934a0d542b8ff7d89e6e98b5e43db9c6a33dd2a21a19a20e1b9ce61b98880bba9b126a740cf0eddc6e","name":"fed.json","type":"application/json","lastModified":1573843111887.136,"size":1043417}] 31:{"id":"2ceaec0b49ada8c8","slug":"introduction-to-leaflet-and-d3","title":"Introduction to leaflet and D3","thumbnail":"9f79f3661154aaec73bfcde493c0518abf1f2ded0f433a3ef971129ed8f9e2f9","access_level":"public","create_time":"$D2019-11-15T18:33:33.876Z","update_time":"$D2019-11-15T19:46:38.335Z","view_time":null,"first_public_time":"$D2019-11-15T19:47:33.984Z","has_unpublished_edits":null,"fork":{"id":"8e39c187b0416390","slug":"introduction-to-leaflet-and-d3/2","title":"Introduction to leaflet and D3","owner":{"id":"bb76b04514ce3a89","login":"sfu-iat355","name":"IAT355"}},"stars":10,"starred":false,"owner":{"type":"team","id":"cad058e826454c3a","login":"lilpeasant","name":"","avatar_url":"https://avatars-next.observableusercontent.com/acdc9280bf7d54bd455092fbfe0696f415907848d922c8a00a2a3b43625c2318","tier":"starter_2024"},"version":475,"publish_version":475,"role":null,"authored":false,"authors":[{"type":"individual","id":"df4bdc62eb42e4c4","login":"lilpeasant","name":"","avatar_url":"https://avatars-next.observableusercontent.com/acdc9280bf7d54bd455092fbfe0696f415907848d922c8a00a2a3b43625c2318","tier":null}],"members":[{"type":"individual","id":"df4bdc62eb42e4c4","login":"lilpeasant","name":"","avatar_url":"https://avatars-next.observableusercontent.com/acdc9280bf7d54bd455092fbfe0696f415907848d922c8a00a2a3b43625c2318","tier":null,"role":"editor"}],"comments":[],"custom_thumbnail":false,"trashed":false,"lapsed":null,"subscribed":null,"forks":10,"collection":null,"type":"notebook","body":{"title":"Introduction to leaflet and D3","cells":[{"id":0,"value":"md`# Introduction to leaflet and D3`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":17,"value":"md`# Leaflet\n\n[Leaflet](http://leafletjs.com/) is a library for embedding maps on websites. Up until now, we have used vega which plots spatial files on a blank canvas and has limited interaction. There are no background tiles(basemaps) which have to change based on zoom level and what part of the map is in view. In order to utilize a map that supports zooming and panning (like in google maps), we have to use a tile map server that provides these data. Leaflet automatically allows users to connect to tile map servers and other GIS data servers to create maps where user can zoom, pan, and add interactive layers on top. Including a leaflet map on observable has its own unique requirements:\n\n## Including Leaflet\n\n1. First, include the Leaflet JavaScript with \\`require()\\` to pull it from https://unpkg.com\n2. Also include Leaflet's required CSS as a link tag, also pulling from unpkg.`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":21,"value":"L = require('leaflet@1.2.0')","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":23,"value":"html``","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":172,"value":"md` ## Preparing data for leaflet\nLeaflet unfortunately does not allow you to use TopoJson files. You will have to convert them to geoJson for use in leaflet. There are many ways to do this, but a quick an easy way is to use [mapshaper.org](http://mapshaper.org/). Download the TopoJson below and open mapshaper. Here, I am using a new feature in observable [file attachment](https://observablehq.com/@observablehq/file-attachments), which allows you to upload files to be hosted in your notebook as long as they are below 15 MB. use ctr-shift-U or cmd-shift-U to upload document in a cell.`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":181,"value":"ElectoralDistricts = FileAttachment(\"feds.json\").json()","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":208,"value":"md` **Challenge:** convert canadian electoral districts to geojson using mapshaper.org`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":415,"value":"Edist = FileAttachment(\"fed.json\").json()","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":25,"value":"md` ## Creating a base map\nHere we create a simple that uses openstreetmaps as a tile server. You can find other base tile maps that suit your needs [here](https://leaflet-extras.github.io/leaflet-providers/preview/). `","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":33,"value":"$33","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":212,"value":"md ` **Challenge:** create a leaflet map of vancouver using a different basemap`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":417,"value":"map2 = {\n let container = DOM.element ('div', { style: `width:${width}px;height:${width/1.6}px` });\n yield container;\n \n \n \n let map = L.map(container).setView([49.234369, -123.010985], 13.5); // initializes the map, sets zoom & coordinates\n let osmLayer = L.tileLayer('https://stamen-tiles-{s}.a.ssl.fastly.net/toner/{z}/{x}/{y}{r}.{ext}', {\n attribution: 'Map tiles by Stamen Design, CC BY 3.0 — Map data © OpenStreetMap contributors',\n subdomains: 'abcd',\n\tminZoom: 0,\n\tmaxZoom: 20,\n\text: 'png'\n }).addTo(map);\n}\n","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":46,"value":"md` ## Adding Data to Map\nLet's take out vancouver neighbourhoods and add them as a layer to leaflet. `","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":58,"value":"VanAreas = FileAttachment(\"VancouverAreaSize.json\").json()","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":64,"value":"VanAreasMap = {\n\n let container = DOM.element('div', { style: `width:${width}px;height:${width/1.6}px` });\n \n yield container;\n \n\n let map = L.map(container);\n let osmLayer = L.tileLayer('https://{s}.tile.openstreetmap.org/{z}/{x}/{y}.png', {\n attribution: '© OpenStreetMap contributors'\n }).addTo(map); \n \n let VanAreasLayer = L.geoJson(VanAreas, {\n weight: 5, \n color: \"#432\",\n }).bindPopup(function (Layer) {\n return Layer.feature.properties.NAME;\n }).addTo(map);\n \n map.fitBounds(VanAreasLayer.getBounds());\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":215,"value":"md` **Challenge:** Create map of Canada's electoral districts using the file you converted into GeoJson previously`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":439,"value":"map3 = {\n let container = DOM.element ('div', { style: `width:${width}px;height:${width/1.6}px` });\n yield container;\n \n let map = L.map(container); // initializes the map, sets zoom & coordinates\n let osmLayer = L.tileLayer('https://stamen-tiles-{s}.a.ssl.fastly.net/toner/{z}/{x}/{y}{r}.{ext}', {\n attribution: 'Map tiles by Stamen Design, CC BY 3.0 — Map data © OpenStreetMap contributors',\n subdomains: 'abcd',\n\tminZoom: 0,\n\tmaxZoom: 20,\n\text: 'png'\n }).addTo(map);\n \n let EdistLayer = L.geoJson(Edist, {\n weight: 2, \n color: \"#F00\",\n }).bindPopup(function (Layer) {\n return Layer.feature.properties.FEDNAME;\n }).addTo(map);\n\n \n map.fitBounds(EdistLayer.getBounds());\n}\n","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":167,"value":"md` ## D3\nWe are now moving into [D3](https://d3js.org/). D3 is a large library that takes a long time to master, and has lot of idiosyncracies with how it functions. You will notice that there are limits to what you can do in Vega-Lite, and that is also true in Vega (which we have not spent much time on). Instead, we are going to jump straight into D3. Vega-lite and Vega are especially limited in their ability to perform various mapping operations. As you have seen, from the example above, one of those is being able to bring in map tiles and support zooming and panning across many zoom levels and have a relatively seamless experience while doing so. D3.js gives you the flexibility to implement the features that you feel you may need (although, the development time to do so may take longer than you may want). To introduce d3.js, we will be making a very simple dot map.`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":225,"value":"Wcities = FileAttachment(\"map.geojson\").json()","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":232,"value":"$34","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":305,"value":"md`This is great, but we have no base map. We could draw a base map in d3, but what is much better is to combine d3 with leaflet. This allows us all of the functionality of leaflet (without having to reinvent the wheel), along with the flexibility of D3.js to let us do what we like with it.`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":310,"value":"WesternCanadianCities = {\n let container = DOM.element('div', { style: `width:${width}px;height:${width/1.6}px` });\n \n yield container;\n \n\n let map = L.map(container).fitBounds(L.geoJson(Wcities).getBounds());\n let osmLayer = L.tileLayer('https://{s}.tile.openstreetmap.org/{z}/{x}/{y}.png', {\n attribution: '© OpenStreetMap contributors'\n }).addTo(map); \n\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":88,"value":"md`\nHere is another map using polygons. This example gets a bit more complicated. You are free to look at it and play with it. We are going to be covering more complex topics next tutorial.`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":115,"value":"$35","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":392,"value":"md`## Next Week\n* Adding interaction and filtering\n* Selections and Data Binding\n* Linking, filtering, and brushing`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":44,"value":"md` ### Appendix\n* [Tom Macwright's Leaflet](https://observablehq.com/@tmcw/leaflet)\n* [Canada I + leaflet](https://observablehq.com/@mikelotis/canada-i-leaflet)\n* [d3 + leaflet](https://observablehq.com/@idris-maps/leaflet-et-d3)\n`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":119,"value":"md ` ## Imports`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":123,"value":"d3 = require('d3@5')","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":126,"value":"VegaLite = require('vega-embed@6')","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":193,"value":"fedUnemployment = d3.csv(\"https://gist.githubusercontent.com/mbarison/8ab5b4ef36ade1c6cfd05fb2a680d8f0/raw/4a54f7934ceab051a61fda996c8d58da72693fb8/canada_fed_unemp.csv\")","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"}],"files":"$W36","stdlib":"1","titling":"auto"}} 32:"$31:body"