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D3.js geoMercator() Function
  • Last Updated : 01 Oct, 2020

D3.js is a JavaScript library for producing dynamic, interactive data visualizations in web browsers. It makes use of Scalable Vector Graphics, HTML5, and Cascading Style Sheets standards. The geoMercator() function in d3.js is used to draw The spherical Mercator projection.

Syntax:

d3.geoMercator()

Parameters: This method does not accept any parameters.

Returns: This method creates the Mercator projection from given json data.

Example #1: The following example draws Mercator projection of world with center at (0, 0) and 0 rotation.



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<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="UTF-8" />
        <meta
            name="viewport"
            content="width=device-width, 
                initial-scale=1.0"
        />
    </head>
  
    <body>
        <div style="width: 700px; height: 500px;">
            <center>
                <h3 style="color: black;"></h3>
            </center>
  
            <svg width="600" 
                 height="450"></svg>
        </div>
        <script src="https://d3js.org/d3.v4.js"></script>
        <script src=
                "https://d3js.org/d3-geo-projection.v2.min.js">
      </script>
        <script>
            var svg = d3.select("svg"),
                width = +svg.attr("width"),
                height = +svg.attr("height");
  
            // Mercator projection
            // Center(0, 0) with 0 rotation
            var gfg = d3
                .geoMercator()
                .scale(width / 2.5 / Math.PI)
                .rotate([0, 0])
                .center([0, 0])
                .translate([width / 2, height / 2]);
  
            // Loading the json data
            // Used json file stored at
             /datageojson/master/world.json*/
            d3.json(
              function (data) {
                // Drawing the map
                svg.append("g").selectAll(
                  "path").data(data.features).enter().append(
                  "path").attr("fill", "black").attr(
                  "d", d3.geoPath().projection(gfg)).style(
                  "stroke", "#ffff");
            });
        </script>
    </body>
</html>

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Output:

Mercator  projection of World with no rotation and centered at (0, 0)

Example #2: The following example draws Mercator projection of world after altering the center and rotation.

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<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="UTF-8" />
        <meta
            name="viewport"
            content="width=device-width, 
                initial-scale=1.0"
        />
    </head>
  
    <body>
        <div style="width: 700px; height: 600px;">
            <center>
                <h3 style="color: black;"></h3>
            </center>
  
            <svg width="500" height="450"></svg>
        </div>
        <script src="https://d3js.org/d3.v4.js"></script>
        <script src=
             "https://d3js.org/d3-geo-projection.v2.min.js">
      </script>
        <script>
            var svg = d3.select("svg"),
                width = +svg.attr("width"),
                height = +svg.attr("height");
  
            // Mercator  projection
 // Center(20, 20) and 90 degree rotation w.r.t Y axis
            var gfg = d3
                .geoMercator()
                .scale(width / 2.5 / Math.PI)
                .rotate([90, 0])
                .center([20, 20])
                .translate([width / 2, height / 2]);
  
            // Loading the json data
            // Used json file stored at 
            /datageojson/master/world.json*/
            d3.json(
              function (data) {
                // Draw the map
                svg.append("g").selectAll(
                  "path").data(data.features).enter().append(
                  "path").attr("fill", "Turquoise").attr(
                  "d", d3.geoPath().projection(gfg)).style(
                  "stroke", "#ffff");
            });
        </script>
    </body>
</html>

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Output:

Mercator projection with 90 degree rotation w.r.t  Y axis  and centered at (20, 20)

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