India Mercator

Draw a map of India with D3.js, Topojson, and five simple functions:

centerZoom - Automatically centers and scales your map to its container, and returns your map's outer boundaries in case you want to draw them.
drawOuterBoundary - Uses the boundary returned from centerZoom to draw a boundary around your whole map.
drawPlaces - Draws place names, if your topojson has places.
drawSubunits - Draws subunits.
colorSubunits - Colors the subunits.

This map uses a Mercator projection, and the colors are generated from d3.schemeCategory20. For a tutorial on converting Geojson to Topojson and for finding the coordinates of major cities, see this tutorial.

<!DOCTYPE html>
<html>
  <head>
    <style>
    body {
      font-family: "Helvetica Neue", sans-serif;
      margin: 0;
    }
    </style>
  </head>
  <body>
    <script src="https://d3js.org/d3.v4.min.js"></script>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/topojson/1.6.20/topojson.min.js"></script>
    <script>
    var width = window.innerWidth, height = window.innerHeight;

var projection = d3.geoMercator();

var path = d3.geoPath()
        .projection(projection)
        .pointRadius(2);

var svg = d3.select("body").append("svg")
        .attr("width", width)
        .attr("height", height);

var g = svg.append("g");

d3.json("india.json", function(error, data){

var boundary = centerZoom(data);
      var subunits = drawSubUnits(data);
      colorSubunits(subunits);
      drawSubUnitLabels(data);
      drawPlaces(data);
      drawOuterBoundary(data, boundary);

});

function centerZoom(data){

var o = topojson.mesh(data, data.objects.polygons, function(a, b) { return a === b; });

projection
          .scale(1)
          .translate([0, 0]);

var b = path.bounds(o),
          s = 1 / Math.max((b[1][0] - b[0][0]) / width, (b[1][1] - b[0][1]) / height),
          t = [(width - s * (b[1][0] + b[0][0])) / 2, (height - s * (b[1][1] + b[0][1])) / 2];

var p = projection
          .scale(s)
          .translate(t);

return o;

}

function drawOuterBoundary(data, boundary){

g.append("path")
          .datum(boundary)
          .attr("d", path)
          .attr("class", "subunit-boundary")
          .attr("fill", "none")
          .attr("stroke", "#3a403d");

}

function drawPlaces(data){

g.append("path")
          .datum(topojson.feature(data, data.objects.places))
          .attr("d", path)
          .attr("class", "place");

g.selectAll(".place-label")
          .data(topojson.feature(data, data.objects.places).features)
        .enter().append("text")
          .attr("class", "place-label")
          .attr("transform", function(d) { return "translate(" + projection(d.geometry.coordinates) + ")"; })
          .attr("dy", ".35em")
          .attr("x", 6)
          .attr("text-anchor", "start")
          .style("font-size", ".7em")
          .style("text-shadow", "0px 0px 2px #fff")
          .text(function(d) { return d.properties.name; });

}

function drawSubUnits(data){

var subunits = g.selectAll(".subunit")
          .data(topojson.feature(data, data.objects.polygons).features)
        .enter().append("path")
          .attr("class", "subunit")
          .attr("d", path)
          .style("stroke", "#fff")
          .style("stroke-width", "1px");

return subunits;

}

function drawSubUnitLabels(data){

g.selectAll(".subunit-label")
          .data(topojson.feature(data, data.objects.polygons).features)
        .enter().append("text")
          .attr("class", "subunit-label")
          .attr("transform", function(d) { return "translate(" + path.centroid(d) + ")"; })
          .attr("dy", ".35em")
          .attr("text-anchor", "middle")
          .style("font-size", ".5em")
          .style("text-shadow", "0px 0px 2px #fff")
          .style("text-transform", "uppercase")
          .text(function(d) { return d.properties.st_nm; });

}

function colorSubunits(subunits) {

var c = d3.scaleOrdinal(d3.schemeCategory20);
      subunits
          .style("fill", function(d,i){ return c(i); })
          .style("opacity", ".6");

}
    </script>

</body>
</html>

https://d3js.org/d3.v4.min.js

https://cdnjs.cloudflare.com/ajax/libs/topojson/1.6.20/topojson.min.js