mbostock/.block

## .block
license: gpl-3.0
redirect: https://observablehq.com/@d3/zoomable-raster-vector

## README.md

      
        
                
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              README.md
            
          
        
      
      
    Using d3-tile to display raster image tiles underneath some TopoJSON vectors, and d3-zoom for pan & zoom. This version adjusts the transform and stroke-width to update the displayed vector data efficiently. You can instead reproject interactively, but changing the transform is typically much faster. Also see the static version.
Tiles copyright OpenStreetMap contributors.

  

  

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

body {
  margin: 0;
}

path {
  fill: none;
  stroke: red;
  stroke-linejoin: round;
  stroke-width: 1.5px;
}

</style>
<svg></svg>
<script src="//d3js.org/d3.v4.min.js"></script>
<script src="//d3js.org/d3-tile.v0.0.min.js"></script>
<script src="//d3js.org/topojson.v1.min.js"></script>
<script>

var pi = Math.PI,
    tau = 2 * pi;

var width = Math.max(960, window.innerWidth),
    height = Math.max(500, window.innerHeight);

// Initialize the projection to fit the world in a 1×1 square centered at the origin.
var projection = d3.geoMercator()
    .scale(1 / tau)
    .translate([0, 0]);

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

var tile = d3.tile()
    .size([width, height]);

var zoom = d3.zoom()
    .scaleExtent([1 << 11, 1 << 14])
    .on("zoom", zoomed);

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

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

var vector = svg.append("path");

d3.json("/mbostock/raw/4090846/us.json", function(error, us) {
  if (error) throw error;

  // Compute the projected initial center.
  var center = projection([-98.5, 39.5]);

  // Apply a zoom transform equivalent to projection.{scale,translate,center}.
  svg
      .call(zoom)
      .call(zoom.transform, d3.zoomIdentity
          .translate(width / 2, height / 2)
          .scale(1 << 12)
          .translate(-center[0], -center[1]));

  vector
      .attr("d", path(topojson.mesh(us, us.objects.counties)));
});

function zoomed() {
  var transform = d3.event.transform;

  var tiles = tile
      .scale(transform.k)
      .translate([transform.x, transform.y])
      ();

  vector
      .attr("transform", transform)
      .style("stroke-width", 1 / transform.k);

  var image = raster
      .attr("transform", stringify(tiles.scale, tiles.translate))
    .selectAll("image")
    .data(tiles, function(d) { return d; });

  image.exit().remove();

  image.enter().append("image")
      .attr("xlink:href", function(d) { return "http://" + "abc"[d[1] % 3] + ".tile.openstreetmap.org/" + d[2] + "/" + d[0] + "/" + d[1] + ".png"; })
      .attr("x", function(d) { return d[0] * 256; })
      .attr("y", function(d) { return d[1] * 256; })
      .attr("width", 256)
      .attr("height", 256);
}

function stringify(scale, translate) {
  var k = scale / 256, r = scale % 1 ? Number : Math.round;
  return "translate(" + r(translate[0] * scale) + "," + r(translate[1] * scale) + ") scale(" + k + ")";
}

</script>

## preview.png

      
        
                
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              preview.png
            
          
        
      
    
    

        
            
        
    

  

## thumbnail.png

      
        
                
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              thumbnail.png
	license: gpl-3.0
	redirect: https://observablehq.com/@d3/zoomable-raster-vector
	<!DOCTYPE html>
	<meta charset="utf-8">
	<style>

	body {
	margin: 0;
	}

	path {
	fill: none;
	stroke: red;
	stroke-linejoin: round;
	stroke-width: 1.5px;
	}

	</style>
	<svg></svg>
	<script src="//d3js.org/d3.v4.min.js"></script>
	<script src="//d3js.org/d3-tile.v0.0.min.js"></script>
	<script src="//d3js.org/topojson.v1.min.js"></script>
	<script>

	var pi = Math.PI,
	tau = 2 * pi;

	var width = Math.max(960, window.innerWidth),
	height = Math.max(500, window.innerHeight);

	// Initialize the projection to fit the world in a 1×1 square centered at the origin.
	var projection = d3.geoMercator()
	.scale(1 / tau)
	.translate([0, 0]);

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

	var tile = d3.tile()
	.size([width, height]);

	var zoom = d3.zoom()
	.scaleExtent([1 << 11, 1 << 14])
	.on("zoom", zoomed);

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

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

	var vector = svg.append("path");

	d3.json("/mbostock/raw/4090846/us.json", function(error, us) {
	if (error) throw error;

	// Compute the projected initial center.
	var center = projection([-98.5, 39.5]);

	// Apply a zoom transform equivalent to projection.{scale,translate,center}.
	svg
	.call(zoom)
	.call(zoom.transform, d3.zoomIdentity
	.translate(width / 2, height / 2)
	.scale(1 << 12)
	.translate(-center[0], -center[1]));

	vector
	.attr("d", path(topojson.mesh(us, us.objects.counties)));
	});

	function zoomed() {
	var transform = d3.event.transform;

	var tiles = tile
	.scale(transform.k)
	.translate([transform.x, transform.y])
	();

	vector
	.attr("transform", transform)
	.style("stroke-width", 1 / transform.k);

	var image = raster
	.attr("transform", stringify(tiles.scale, tiles.translate))
	.selectAll("image")
	.data(tiles, function(d) { return d; });

	image.exit().remove();

	image.enter().append("image")
	.attr("xlink:href", function(d) { return "http://" + "abc"[d[1] % 3] + ".tile.openstreetmap.org/" + d[2] + "/" + d[0] + "/" + d[1] + ".png"; })
	.attr("x", function(d) { return d[0] * 256; })
	.attr("y", function(d) { return d[1] * 256; })
	.attr("width", 256)
	.attr("height", 256);
	}

	function stringify(scale, translate) {
	var k = scale / 256, r = scale % 1 ? Number : Math.round;
	return "translate(" + r(translate[0] * scale) + "," + r(translate[1] * scale) + ") scale(" + k + ")";
	}

	</script>