Wikiatlas Localisator using D3.geo

A complete, automatic and flexible orthographic localisator for Wikipedia maps.

var bb = { "item":"India", "W": 67.0, "N":37.5, "E": 99.0, "S": 5.0 }, 
localisator("body", 200, bb.item, bb.W, bb.N, bb.E, bb.S);

It take as input :

a JS selector: a target html element's selector such as "body", "#hook", to be appended to,
a width (px),
the item name (string),
four geocoordinates (decimal degrees), representing the bounding box ordered as West, North, East, South.

The style approximate most recent Wikipedia localisator map guidelines.

The first issue was to move away from straight lines to correctly curved lines.

enter image description here

The second issue was to support bounding boxes upon the 180⁰ meridians. Boxes upon the 180th meridian need special management. By example, localising a set of pacific islands between 155⁰ East and -155 West initially gives....

enter image description here

...with correct rotation (+180⁰) :

enter image description here

... and with correct boxing:

enter image description here

Localisator now perfect, enjoy !

![enter image description here][7] [7]: http://i.stack.imgur.com/Vc0qK.png

For technical details, see code and D3.geo : Spherical arcs rather than straight lines for paralles?. For deeper documentation, see D3.geo and bounding boxes.

<!DOCTYPE html>
<meta charset="utf-8">
<body>
<script src="//code.jquery.com/jquery-2.1.0.min.js"></script>
<script src="//cdnjs.cloudflare.com/ajax/libs/d3/3.4.13/d3.min.js"></script>
<script src="//cdnjs.cloudflare.com/ajax/libs/topojson/1.1.0/topojson.min.js"></script>
<script src="//cdnjs.cloudflare.com/ajax/libs/d3-geo-projection/0.2.9/d3.geo.projection.min.js"></script>
	
<script src="../js/wikiatlas.js"></script>
	<style>svg { border: 1px solid #BBB; }</style>
<script>

/**
* Created with Wikiatlas.
* User: hugolpz
* version: 2015.01.21 */
	
/* ****************************************************** */
/* MATH TOOLKIT ***************************************** */
function parallel(φ, λ0, λ1) {
  if (λ0 > λ1) λ1 += 360;
  var dλ = λ1 - λ0,
      step = dλ / Math.ceil(dλ);
  return d3.range(λ0, λ1 + 0.5 * step, step).map(function(λ) { return [normalise(λ), φ]; });
}
function normalise(x) {
  return (x + 180) % 360 - 180;
}
/* ****************************************************** */
/* LOCALISATOR FN *************************************** */
var localisator = function (hookId,localisator_width, title, WNES0, WNES1, WNES2, WNES3) {
/* Init ************************************************* */
	var width  = 1*localisator_width,
    	height = 1*localisator_width;
	var lon_central = function(){ 
		var num;
		if(WNES2<WNES0){ num= -(WNES0+WNES2)/2+180; }
		else{ num= -(WNES0+WNES2)/2; }
		return num;
	};

var proj = d3.geo.orthographic()
    	.scale(1/2*localisator_width)
    	.rotate([ lon_central(), -(WNES1+WNES3)/2 +10 ]); // orthographic + 10⁰ to simulate real life globe watching.

var projection2 = proj
		.translate([width / 2 , height / 2 ])
		.clipAngle(90);

var path = d3.geo.path()
		.projection(projection2);

/* SVG container **************************************** */
	var svg = d3.select(hookId).append("svg")
		.attr("id", title+"-orthographic_globe_locator_(wikiatlas_2014)")
		.attr("width", width)
		.attr("height", height)
		.call(d3.behavior.drag()
		  .origin(function() { 
			var rotate = projection2.rotate(); 
			return {x: 2 * rotate[0], y: -2 * rotate[1]}; 
		})
		  .on("drag", function() {
			projection2.rotate([d3.event.x / 2, -d3.event.y / 2, projection2.rotate()[2]]);
			svg.selectAll("path").attr("d", path);
		  }))
		.on("dblclick", function() {
			projection2.rotate([ lon_central(), -(WNES1+WNES3)/2 +10 ]);
			svg.selectAll("path").attr("d", path);
		});

/* SVG background *************************************** */
// Blue circle
	svg.append("circle")
		.attr("class", "water")
		.attr("cx", width/2)
		.attr("cy", height/2)
		.attr("r", width/2 )
		.style({'fill':'#C6ECFF'})
		.style({'stroke': '656565', 'stroke-width': 1.5});
	// Gradiant	settings
	var gradient = svg.append("svg:defs")
		.append("svg:linearGradient")
		.attr("id", "gradient")
		.attr("x1", "0%")
		.attr("y1", "0%")
		.attr("fx1", "30%")
		.attr("fy1", "30%")
		.attr("x2", "100%")
		.attr("y2", "100%")
		.attr("spreadMethod", "pad");
	gradient.append("svg:stop") 		// middle step setting
		.attr("offset", "50%")
		.attr("stop-color", "#FFF")
		.attr("stop-opacity", 0.3);
	gradient.append("svg:stop") 		// final step setting
		.attr("offset", "100%")
		.attr("stop-color", "#009")
		.attr("stop-opacity", 0.3);
	// Gradiant-circle
	var circle = svg.append('circle') 	// append gradient to circle
		.attr('cx', width / 2)
		.attr('cy', height / 2)
		.attr('r', width/2 )
		.attr('fill', 'url(#gradient)');
	
	
/* ****************************************************** */
/* GIS data injection *********************************** */
d3.json("world-110m-ids.json", function(error, world) {
	var country = svg.selectAll(".country")
		.data(topojson.feature(world, world.objects.countries).features)
	.enter().append("path")
		.attr("id", function(d){ return d.id } )
		.attr("class", "country")
		.style("fill", "#FDFBEA")
		.attr("d", path);
	
	var	focus = d3.selectAll("#"+title)
			.style("fill", "#B10000"); 
	
	var boundaries = svg.append("path")
        //.datum( topojson.mesh(world, world.objects.countries, function(a,b) { if (a!==b){var ret = b;}return ret;}))
		.datum( topojson.mesh(world, world.objects.countries, function(a,b) { return a!==b; }))
		.attr("class", "boundary")
		.attr("d", path)
		.style({'fill':'none','stroke': '#656565', 'stroke-width': 0.5});
	
	var graticule = svg.append("path")
		.datum(d3.geo.graticule().step([20,20]))
		.attr("class", "graticule")
		.attr("d", path)
		.style({'fill':'none', 'stroke':'#777', 'stroke-width': 0.5, 'stroke-opacity': 0.5});

};

var WNES = { "item":"India", "W": 67.0, "N":37.5, "E": 99.0, "S": 5.0 };
localisator("body",500, WNES.item, WNES.W, WNES.N, WNES.E, WNES.S);
</script>

https://code.jquery.com/jquery-2.1.0.min.js

https://cdnjs.cloudflare.com/ajax/libs/d3/3.4.13/d3.min.js

https://cdnjs.cloudflare.com/ajax/libs/topojson/1.1.0/topojson.min.js

https://cdnjs.cloudflare.com/ajax/libs/d3-geo-projection/0.2.9/d3.geo.projection.min.js