Zoom Buttons I

This example shows how to implement zoom in and zoom out buttons on a map using D3 and SVG transforms. Once the target scale and translation are computed, the map transitions over 350ms.

This is a fork Mike Bostock's Map Pan & Zoom I; you can diff the two to see my changes. The scaling math (which is quite tricky!) is derived from Wil Linssen.

If zooming by a hard-coded factor would push the scale beyond the scale extent, it is clipped. Importantly, this clipping also affects the translation. If you scale by 1.047 but translate as if you had scaled by 1.2, bad things happen.

See also Zoom Buttons II.

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

svg {
  background: #eee;
}

.sphere {
  fill: #fff;
}

.land {
  fill: #000;
}

.boundary {
  fill: none;
  stroke: #fff;
  stroke-linejoin: round;
  stroke-linecap: round;
  vector-effect: non-scaling-stroke;
}

.overlay {
  fill: none;
  pointer-events: all;
}

</style>
<script src="https://d3js.org/d3.v3.min.js"></script>
<script src="https://d3js.org/topojson.v1.min.js"></script>
<body>
<script>

var width = 960,
    height = 960,
    center = [width / 2, height / 2];

var projection = d3.geo.mercator()
    .translate([width / 2, height / 2])
    .scale((width - 1) / 2 / Math.PI);

var zoom = d3.behavior.zoom()
    .scaleExtent([1, 8])
    .on("zoom", zoomed);

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

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

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

svg.append("rect")
    .attr("class", "overlay")
    .attr("width", width)
    .attr("height", height);

svg
    .call(zoom)
    .call(zoom.event);

d3.json("/../../data/world-50m.json", function(error, world) {
  g.append("path")
      .datum({type: "Sphere"})
      .attr("class", "sphere")
      .attr("d", path);

g.append("path")
      .datum(topojson.merge(world, world.objects.countries.geometries))
      .attr("class", "land")
      .attr("d", path);

g.append("path")
      .datum(topojson.mesh(world, world.objects.countries, function(a, b) { return a !== b; }))
      .attr("class", "boundary")
      .attr("d", path);
});

function zoomed() {
  g.attr("transform", "translate(" + zoom.translate() + ")scale(" + zoom.scale() + ")");
}

d3.select(self.frameElement).style("height", height + "px");

// Simplest possible buttons
svg.selectAll(".button")
    .data(['zoom_in', 'zoom_out'])
    .enter()
    .append("rect")
    .attr("x", function(d,i){return 10 + 50*i})
    .attr({y: 10, width: 40, height: 20, class: "button"})
    .attr("id", function(d){return d})
    .style("fill", function(d,i){ return i ? "red" : "green"})

d3.selectAll('.button').on('click', function(){
    d3.event.preventDefault();

var scale = zoom.scale(),
        extent = zoom.scaleExtent(),
        translate = zoom.translate(),
        x = translate[0], y = translate[1],
        factor = (this.id === 'zoom_in') ? 1.2 : 1/1.2,
        target_scale = scale * factor;

// If we're already at an extent, done
    if (target_scale === extent[0] || target_scale === extent[1]) { return false; }
    // If the factor is too much, scale it down to reach the extent exactly
    var clamped_target_scale = Math.max(extent[0], Math.min(extent[1], target_scale));
    if (clamped_target_scale != target_scale){
        target_scale = clamped_target_scale;
        factor = target_scale / scale;
    }

// Center each vector, stretch, then put back
    x = (x - center[0]) * factor + center[0];
    y = (y - center[1]) * factor + center[1];

// Transition to the new view over 350ms
    d3.transition().duration(350).tween("zoom", function () {
        var interpolate_scale = d3.interpolate(scale, target_scale),
            interpolate_trans = d3.interpolate(translate, [x,y]);
        return function (t) {
            zoom.scale(interpolate_scale(t))
                .translate(interpolate_trans(t));
            zoomed();
        };
    });
});

</script>

Modified http://d3js.org/d3.v3.min.js to a secure url

Modified http://d3js.org/topojson.v1.min.js to a secure url

Changed /mbostock/raw/4090846/world-50m.json to a local referenece

https://d3js.org/d3.v3.min.js

https://d3js.org/topojson.v1.min.js