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4 Steps to Creating Overlays

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Over the last few months, Intridea has worked on several projects revolving around charts, maps, and interactive stats. Learning how to effectively display these aspects, both at a functional and beautiful level, is a challenging task. However, like the old saying goes, necessity is the mother of invention, and these projects taught us some unique ways to streamlining the overlay process…

The Challenge:
Effectively display data stats and implement maps with a highlight overlay for maps to draw attention to one and/or a few specific countries.

The Solution:
After some research, we chose Mapbox as the base map, enabling easier customization in the shaded area/border/ocean colors, and for the overlay, utilizing d3 to add a highlight layer. Here’s the 4 step process:

Step 1: Initiate Mapbox map on specify div:

var map = L.mapbox.map("country_map", ‘your_mapbox_map_id');  

Step 2: Add a base layer to the map with custom styles:

    var layer = L.geoJson(null, { style: { fillColor: '#c6bbaf', fillOpacity: 0.5, weight: 0, color: '#ffffff', opacity: 1 }})     map.addLayer(layer)  

In order to complete Step 2, we created detailed geojsons for each country, either by generating from a shapefile or creating manually from http://geojson.io.

Step 3: Use d3 to load country geojson and set bounds to country area:

    var json_file = "/assets/" + country_isocode + ".json"     d3.json(json_file, function(error, data){            layer.addData(data.features);            map.fitBounds(layer.getBounds());     } 

Step 4: Add a marker on country capital and create an anchor to correctly position display:

           var latLng = L.latLng(lat, lng);       var pinAnchor = new L.Point(8, 8);       var pinAnchor = new L.Point(8, 8);       var icon = L.icon({         iconUrl: "/assets/icon-star.png",         iconAnchor: pinAnchor       }); 


Feel free to utilize this process! Click here to download the countries geojson.

Resources:

  • http://diva-gis.org
  • http://leafletjs.com (mapbox 1.0 use leafletjs as base api)
  • http://geojson.io
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