simplified borders by fil

index.html

<!DOCTYPE html>
<meta charset="utf-8">
<style>

body {
  background: white;
}

.stroke {
  fill: none;
  stroke: #000;
  stroke-width: 1.5px;
}

.fill {
  fill: #fff;
}

.graticule {
  fill: none;
  stroke: #777;
  stroke-width: .5px;
  stroke-opacity: .5;
}

.land {
  fill: #222;
}

.boundary {
  fill: none;
  stroke: #fff;
  stroke-width: .5px;
}

</style>
<body>
<script src="https://d3js.org/d3.v4.min.js"></script>
<script src="topojson-client.js"></script>
<script>

var width = 960,
    height = 580;

var color = d3.scaleOrdinal(d3.schemeCategory20c);

var projection = d3.geoOrthographic();

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


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

  color('coast'); // fix coast line = color[0] = blue.
  
d3.json("https://ipfs.io/ipfs/QmQEGopkuSzCmEWXZHTLvvRnYJk9ioA53HLP76FhWrrzvK/topojson/110m.json", function(error, world) {
  if (error) throw error;

  var countries = topojson.feature(world, world.objects.countries).features,
      neighbors = topojson.neighbors(world.objects.countries.geometries);
  
  var borders = topojson.meshes(
    world,
    world.objects.countries,
    (a,b) => a == b ? 'coast' : d3.extent([a.id, b.id]) 
  );
  
  // simplify each border segment
  var b = borders.features 
  .map(d => {
    if (d.properties.tag !== 'coast')
    d.geometry.coordinates = d.geometry.coordinates.
    map(a => [ a[0], a[a.length-1]]); 
    return d;
  });
  
svg.selectAll('.border')
.data(b)
.enter()
.append('path')
.attr('d', path)
.attr('fill', 'none')
.attr('stroke', d => color(''+d.properties.tag))
.attr('stroke-width', d => d.properties.tag == 'coast' ? 2 : 1)

svg.append('path')
.datum({type:"Sphere"})
.attr('d', path)
.attr('class', 'stroke')

});

  d3.timer(e => {
    projection.rotate([e/150])
    svg.selectAll('path').attr('d', path)
  }, 100)
  

</script>

topojson-client.js

// https://github.com/topojson/topojson-client Version 3.0.0. Copyright 2017 Mike Bostock.
(function (global, factory) {
	typeof exports === 'object' && typeof module !== 'undefined' ? factory(exports) :
	typeof define === 'function' && define.amd ? define(['exports'], factory) :
	(factory((global.topojson = global.topojson || {})));
}(this, (function (exports) { 'use strict';

var identity = function(x) {
  return x;
};

var transform = function(transform) {
  if (transform == null) return identity;
  var x0,
      y0,
      kx = transform.scale[0],
      ky = transform.scale[1],
      dx = transform.translate[0],
      dy = transform.translate[1];
  return function(input, i) {
    if (!i) x0 = y0 = 0;
    var j = 2, n = input.length, output = new Array(n);
    output[0] = (x0 += input[0]) * kx + dx;
    output[1] = (y0 += input[1]) * ky + dy;
    while (j < n) output[j] = input[j], ++j;
    return output;
  };
};

var bbox = function(topology) {
  var t = transform(topology.transform), key,
      x0 = Infinity, y0 = x0, x1 = -x0, y1 = -x0;

  function bboxPoint(p) {
    p = t(p);
    if (p[0] < x0) x0 = p[0];
    if (p[0] > x1) x1 = p[0];
    if (p[1] < y0) y0 = p[1];
    if (p[1] > y1) y1 = p[1];
  }

  function bboxGeometry(o) {
    switch (o.type) {
      case "GeometryCollection": o.geometries.forEach(bboxGeometry); break;
      case "Point": bboxPoint(o.coordinates); break;
      case "MultiPoint": o.coordinates.forEach(bboxPoint); break;
    }
  }

  topology.arcs.forEach(function(arc) {
    var i = -1, n = arc.length, p;
    while (++i < n) {
      p = t(arc[i], i);
      if (p[0] < x0) x0 = p[0];
      if (p[0] > x1) x1 = p[0];
      if (p[1] < y0) y0 = p[1];
      if (p[1] > y1) y1 = p[1];
    }
  });

  for (key in topology.objects) {
    bboxGeometry(topology.objects[key]);
  }

  return [x0, y0, x1, y1];
};

var reverse = function(array, n) {
  var t, j = array.length, i = j - n;
  while (i < --j) t = array[i], array[i++] = array[j], array[j] = t;
};

var collection = function(topology, o) {
  return o.type === "GeometryCollection"
      ? {type: "FeatureCollection", features: o.geometries.map(function(o) { return feature(topology, o); })}
      : feature(topology, o);
};

function feature(topology, o) {
  var id = o.id,
      bbox = o.bbox,
      properties = o.properties == null ? {} : o.properties,
      geometry = object(topology, o);
  return id == null && bbox == null ? {type: "Feature", properties: properties, geometry: geometry}
      : bbox == null ? {type: "Feature", id: id, properties: properties, geometry: geometry}
      : {type: "Feature", id: id, bbox: bbox, properties: properties, geometry: geometry};
}

function object(topology, o) {
  var transformPoint = transform(topology.transform),
      arcs = topology.arcs;

  function arc(i, points) {
    if (points.length) points.pop();
    for (var a = arcs[i < 0 ? ~i : i], k = 0, n = a.length; k < n; ++k) {
      points.push(transformPoint(a[k], k));
    }
    if (i < 0) reverse(points, n);
  }

  function point(p) {
    return transformPoint(p);
  }

  function line(arcs) {
    var points = [];
    for (var i = 0, n = arcs.length; i < n; ++i) arc(arcs[i], points);
    if (points.length < 2) points.push(points[0]); // This should never happen per the specification.
    return points;
  }

  function ring(arcs) {
    var points = line(arcs);
    while (points.length < 4) points.push(points[0]); // This may happen if an arc has only two points.
    return points;
  }

  function polygon(arcs) {
    return arcs.map(ring);
  }

  function geometry(o) {
    var type = o.type, coordinates;
    switch (type) {
      case "GeometryCollection": return {type: type, geometries: o.geometries.map(geometry)};
      case "Point": coordinates = point(o.coordinates); break;
      case "MultiPoint": coordinates = o.coordinates.map(point); break;
      case "LineString": coordinates = line(o.arcs); break;
      case "MultiLineString": coordinates = o.arcs.map(line); break;
      case "Polygon": coordinates = polygon(o.arcs); break;
      case "MultiPolygon": coordinates = o.arcs.map(polygon); break;
      default: return null;
    }
    return {type: type, coordinates: coordinates};
  }

  return geometry(o);
}

var stitch = function(topology, arcs) {
  var stitchedArcs = {},
      fragmentByStart = {},
      fragmentByEnd = {},
      fragments = [],
      emptyIndex = -1;

  // Stitch empty arcs first, since they may be subsumed by other arcs.
  arcs.forEach(function(i, j) {
    var arc = topology.arcs[i < 0 ? ~i : i], t;
    if (arc.length < 3 && !arc[1][0] && !arc[1][1]) {
      t = arcs[++emptyIndex], arcs[emptyIndex] = i, arcs[j] = t;
    }
  });

  arcs.forEach(function(i) {
    var e = ends(i),
        start = e[0],
        end = e[1],
        f, g;

    if (f = fragmentByEnd[start]) {
      delete fragmentByEnd[f.end];
      f.push(i);
      f.end = end;
      if (g = fragmentByStart[end]) {
        delete fragmentByStart[g.start];
        var fg = g === f ? f : f.concat(g);
        fragmentByStart[fg.start = f.start] = fragmentByEnd[fg.end = g.end] = fg;
      } else {
        fragmentByStart[f.start] = fragmentByEnd[f.end] = f;
      }
    } else if (f = fragmentByStart[end]) {
      delete fragmentByStart[f.start];
      f.unshift(i);
      f.start = start;
      if (g = fragmentByEnd[start]) {
        delete fragmentByEnd[g.end];
        var gf = g === f ? f : g.concat(f);
        fragmentByStart[gf.start = g.start] = fragmentByEnd[gf.end = f.end] = gf;
      } else {
        fragmentByStart[f.start] = fragmentByEnd[f.end] = f;
      }
    } else {
      f = [i];
      fragmentByStart[f.start = start] = fragmentByEnd[f.end = end] = f;
    }
  });

  function ends(i) {
    var arc = topology.arcs[i < 0 ? ~i : i], p0 = arc[0], p1;
    if (topology.transform) p1 = [0, 0], arc.forEach(function(dp) { p1[0] += dp[0], p1[1] += dp[1]; });
    else p1 = arc[arc.length - 1];
    return i < 0 ? [p1, p0] : [p0, p1];
  }

  function flush(fragmentByEnd, fragmentByStart) {
    for (var k in fragmentByEnd) {
      var f = fragmentByEnd[k];
      delete fragmentByStart[f.start];
      delete f.start;
      delete f.end;
      f.forEach(function(i) { stitchedArcs[i < 0 ? ~i : i] = 1; });
      fragments.push(f);
    }
  }

  flush(fragmentByEnd, fragmentByStart);
  flush(fragmentByStart, fragmentByEnd);
  arcs.forEach(function(i) { if (!stitchedArcs[i < 0 ? ~i : i]) fragments.push([i]); });

  return fragments;
};

var mesh = function(topology) {
  return object(topology, meshArcs.apply(this, arguments));
};

function meshes(topology) {
  return collection(topology, {
    type: "GeometryCollection",
    geometries: meshesArcs.apply(this, arguments)
  });
}

function meshArcs(topology, object$$1, filter) {
  var p, partition = meshesArcs(topology, object$$1, !filter ? null : function() {
    return !!filter.apply(this, arguments);
  });
  return partition.length ? (p = partition[0], delete p.properties, p) : { type: 'MultiLineString', arcs: [] };
}

function meshesArcs(topology, object$$1, tag) {
  var partition, arcs, tags, i, n;

  if (arguments.length > 1) partition = extractArcs(topology, object$$1, tag), tags = partition[1], partition = partition[0];
  else for (i = 0, arcs = new Array(n = topology.arcs.length); i < n; ++i) arcs[i] = i, partition = [arcs], tags = [true];
  
  return partition.map(function(arcs, i) {
    return {
      type: "MultiLineString",
      properties: { tag: tags[i] },
      arcs: stitch(topology, arcs)
    } 
  });
}

function extractArcs(topology, object$$1, tag) {
  var tags = [],
      arcs = [],
      geomsByArc = [],
      geom;

  function extract0(i) {
    var j = i < 0 ? ~i : i;
    (geomsByArc[j] || (geomsByArc[j] = [])).push({i: i, g: geom});
  }

  function extract1(arcs) {
    arcs.forEach(extract0);
  }

  function extract2(arcs) {
    arcs.forEach(extract1);
  }

  function extract3(arcs) {
    arcs.forEach(extract2);
  }
  
  function tagpush(i, tag) {
    if (!tag) return;
    var t = tags.indexOf(tag);
    if (t === -1) tags.push(tag), t = arcs.length, arcs.push([]);
    arcs[t].push(i);
  }

  function geometry(o) {
    switch (geom = o, o.type) {
      case "GeometryCollection": o.geometries.forEach(geometry); break;
      case "LineString": extract1(o.arcs); break;
      case "MultiLineString": case "Polygon": extract2(o.arcs); break;
      case "MultiPolygon": extract3(o.arcs); break;
    }
  }

  geometry(object$$1);

  geomsByArc.forEach(function(geoms) {
    tagpush(geoms[0].i, tag ? tag(geoms[0].g, geoms[geoms.length - 1].g) : true);
  });

  return [arcs, tags];
}

function planarRingArea(ring) {
  var i = -1, n = ring.length, a, b = ring[n - 1], area = 0;
  while (++i < n) a = b, b = ring[i], area += a[0] * b[1] - a[1] * b[0];
  return Math.abs(area); // Note: doubled area!
}

var merge = function(topology) {
  return object(topology, mergeArcs.apply(this, arguments));
};

function mergeArcs(topology, objects) {
  var polygonsByArc = {},
      polygons = [],
      groups = [];

  objects.forEach(geometry);

  function geometry(o) {
    switch (o.type) {
      case "GeometryCollection": o.geometries.forEach(geometry); break;
      case "Polygon": extract(o.arcs); break;
      case "MultiPolygon": o.arcs.forEach(extract); break;
    }
  }

  function extract(polygon) {
    polygon.forEach(function(ring) {
      ring.forEach(function(arc) {
        (polygonsByArc[arc = arc < 0 ? ~arc : arc] || (polygonsByArc[arc] = [])).push(polygon);
      });
    });
    polygons.push(polygon);
  }

  function area(ring) {
    return planarRingArea(object(topology, {type: "Polygon", arcs: [ring]}).coordinates[0]);
  }

  polygons.forEach(function(polygon) {
    if (!polygon._) {
      var group = [],
          neighbors = [polygon];
      polygon._ = 1;
      groups.push(group);
      while (polygon = neighbors.pop()) {
        group.push(polygon);
        polygon.forEach(function(ring) {
          ring.forEach(function(arc) {
            polygonsByArc[arc < 0 ? ~arc : arc].forEach(function(polygon) {
              if (!polygon._) {
                polygon._ = 1;
                neighbors.push(polygon);
              }
            });
          });
        });
      }
    }
  });

  polygons.forEach(function(polygon) {
    delete polygon._;
  });

  return {
    type: "MultiPolygon",
    arcs: groups.map(function(polygons) {
      var arcs = [], n;

      // Extract the exterior (unique) arcs.
      polygons.forEach(function(polygon) {
        polygon.forEach(function(ring) {
          ring.forEach(function(arc) {
            if (polygonsByArc[arc < 0 ? ~arc : arc].length < 2) {
              arcs.push(arc);
            }
          });
        });
      });

      // Stitch the arcs into one or more rings.
      arcs = stitch(topology, arcs);

      // If more than one ring is returned,
      // at most one of these rings can be the exterior;
      // choose the one with the greatest absolute area.
      if ((n = arcs.length) > 1) {
        for (var i = 1, k = area(arcs[0]), ki, t; i < n; ++i) {
          if ((ki = area(arcs[i])) > k) {
            t = arcs[0], arcs[0] = arcs[i], arcs[i] = t, k = ki;
          }
        }
      }

      return arcs;
    })
  };
}

var bisect = function(a, x) {
  var lo = 0, hi = a.length;
  while (lo < hi) {
    var mid = lo + hi >>> 1;
    if (a[mid] < x) lo = mid + 1;
    else hi = mid;
  }
  return lo;
};

var neighbors = function(objects) {
  var indexesByArc = {}, // arc index -> array of object indexes
      neighbors = objects.map(function() { return []; });

  function line(arcs, i) {
    arcs.forEach(function(a) {
      if (a < 0) a = ~a;
      var o = indexesByArc[a];
      if (o) o.push(i);
      else indexesByArc[a] = [i];
    });
  }

  function polygon(arcs, i) {
    arcs.forEach(function(arc) { line(arc, i); });
  }

  function geometry(o, i) {
    if (o.type === "GeometryCollection") o.geometries.forEach(function(o) { geometry(o, i); });
    else if (o.type in geometryType) geometryType[o.type](o.arcs, i);
  }

  var geometryType = {
    LineString: line,
    MultiLineString: polygon,
    Polygon: polygon,
    MultiPolygon: function(arcs, i) { arcs.forEach(function(arc) { polygon(arc, i); }); }
  };

  objects.forEach(geometry);

  for (var i in indexesByArc) {
    for (var indexes = indexesByArc[i], m = indexes.length, j = 0; j < m; ++j) {
      for (var k = j + 1; k < m; ++k) {
        var ij = indexes[j], ik = indexes[k], n;
        if ((n = neighbors[ij])[i = bisect(n, ik)] !== ik) n.splice(i, 0, ik);
        if ((n = neighbors[ik])[i = bisect(n, ij)] !== ij) n.splice(i, 0, ij);
      }
    }
  }

  return neighbors;
};

var untransform = function(transform) {
  if (transform == null) return identity;
  var x0,
      y0,
      kx = transform.scale[0],
      ky = transform.scale[1],
      dx = transform.translate[0],
      dy = transform.translate[1];
  return function(input, i) {
    if (!i) x0 = y0 = 0;
    var j = 2,
        n = input.length,
        output = new Array(n),
        x1 = Math.round((input[0] - dx) / kx),
        y1 = Math.round((input[1] - dy) / ky);
    output[0] = x1 - x0, x0 = x1;
    output[1] = y1 - y0, y0 = y1;
    while (j < n) output[j] = input[j], ++j;
    return output;
  };
};

var quantize = function(topology, transform) {
  if (topology.transform) throw new Error("already quantized");

  if (!transform || !transform.scale) {
    if (!((n = Math.floor(transform)) >= 2)) throw new Error("n must be ≥2");
    box = topology.bbox || bbox(topology);
    var x0 = box[0], y0 = box[1], x1 = box[2], y1 = box[3], n;
    transform = {scale: [x1 - x0 ? (x1 - x0) / (n - 1) : 1, y1 - y0 ? (y1 - y0) / (n - 1) : 1], translate: [x0, y0]};
  } else {
    box = topology.bbox;
  }

  var t = untransform(transform), box, key, inputs = topology.objects, outputs = {};

  function quantizePoint(point) {
    return t(point);
  }

  function quantizeGeometry(input) {
    var output;
    switch (input.type) {
      case "GeometryCollection": output = {type: "GeometryCollection", geometries: input.geometries.map(quantizeGeometry)}; break;
      case "Point": output = {type: "Point", coordinates: quantizePoint(input.coordinates)}; break;
      case "MultiPoint": output = {type: "MultiPoint", coordinates: input.coordinates.map(quantizePoint)}; break;
      default: return input;
    }
    if (input.id != null) output.id = input.id;
    if (input.bbox != null) output.bbox = input.bbox;
    if (input.properties != null) output.properties = input.properties;
    return output;
  }

  function quantizeArc(input) {
    var i = 0, j = 1, n = input.length, p, output = new Array(n); // pessimistic
    output[0] = t(input[0], 0);
    while (++i < n) if ((p = t(input[i], i))[0] || p[1]) output[j++] = p; // non-coincident points
    if (j === 1) output[j++] = [0, 0]; // an arc must have at least two points
    output.length = j;
    return output;
  }

  for (key in inputs) outputs[key] = quantizeGeometry(inputs[key]);

  return {
    type: "Topology",
    bbox: box,
    transform: transform,
    objects: outputs,
    arcs: topology.arcs.map(quantizeArc)
  };
};

exports.bbox = bbox;
exports.feature = collection;
exports.mesh = mesh;
exports.meshes = meshes;
exports.meshArcs = meshArcs;
exports.meshesArcs = meshesArcs;
exports.merge = merge;
exports.mergeArcs = mergeArcs;
exports.neighbors = neighbors;
exports.quantize = quantize;
exports.transform = transform;
exports.untransform = untransform;

Object.defineProperty(exports, '__esModule', { value: true });

})));