rveciana - resizing-polygons-according-to-the-population-density

### Resizing polygons according to the population density

Open raw page in new tab

This example, inspired from Mike Bostock’s Non-contiguous catrogram example, shows the percentage of people in Catalonia able to speak in Catalan in every comarca (data from IDESCAT).

But the Catalan population is not evenly distributed, but concentrated around Barcelona and surroundings. So comparing the region colors can lead to wrong conclusions, since they don’t represent comparable amount of people.

When the Resize to population density button is pressed, the size of each coamrca is reduced according to its population density. The maximum density corresponds to the Barcelonès, which is not reduced. When the sizes are changed is much easier to compare the number of people.

The size is not reduced linearly, but applying the square root, because Catalonia is so unevenly populated that it was difficult so see anything outside Barcelona’s region.

``````<!DOCTYPE html>
<meta charset="utf-8">
<title>Resizing polygons according to the population density</title>
<style>

.background {
fill: None;
stroke: #444;
stroke-width: 1;
}

</style>
<body>
<button type="button" id="changeDensity">Resize to population density</button>
<button type="button" id="changeActual">Resize to actual size</button>
<script src="http://d3js.org/d3.v3.min.js"></script>
<script src="http://d3js.org/topojson.v1.min.js"></script>

<script>
var comarques, color, max_density;
var scaleColors = ['#c2ffbf', '#92ff8c', '#56ff4e', '#20c818'];
var width = 960,
height = 500;

var projection = d3.geo.mercator()
.center([2.1,41.7])
.scale(9000)
.translate([width / 2, height / 2]);

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

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

d3.csv("/rveciana/raw/5919944/comarques.csv", function(data_values) {
max_density = 0;
max_value = 0;
min_value = 100;
for (i=0; i<data_values.length; i++){
if(parseFloat(data_values[i].Density) > max_density){
max_density = parseFloat(data_values[i].Density);
}
if(parseFloat(data_values[i].Catalan) > max_value){
max_value = parseFloat(data_values[i].Catalan);
}
if(parseFloat(data_values[i].Catalan) < min_value){
min_value = parseFloat(data_values[i].Catalan);
}
}

color = d3.scale.quantize(45).domain([min_value,max_value]).range(scaleColors);
console.info(color(min_value));
console.info(color(max_value));
d3.json("/rveciana/raw/5919944/comarques.topo.json", function(error, us) {

comarques = svg.selectAll(".comarca")
.data(topojson.feature(us, us.objects.comarques).features)
.enter().append("path")
.attr("class", "comarca")
.attr("d", path)
.style("fill", function(d) {
return color(parseFloat(data_values[parseInt(d.properties.comarca, 10)-1].Catalan));
})
.style("stroke", function(d) {
return color(parseFloat(data_values[parseInt(d.properties.comarca, 10)-1].Catalan));
});

svg.append("path")
.datum(topojson.feature(us, us.objects.comarques))
.attr("class", "background")
.attr("d", path);

scale = svg.append("g");
scale.append("text")
.attr("x",width - 400 )
.attr("y",height - 50)
.text("Can speak Catalan");
for (i=0; i< scaleColors.length; i++){
scale.append("rect")
.attr("width", 30)
.attr("height",15)
.attr("x",width - 400 + 37*i )
.attr("y",height - 40)
.style("fill",scaleColors[i])
.style("stroke","#000");
scale.append("text")
.attr("x",width - 400 + 37*i )
.attr("y",height - 10)
.text(function(){
return Math.round(min_value + i*(max_value - min_value)/scaleColors.length)+"%";
});

}

d3.select("#changeDensity").on("click", function() {
comarques.transition()
.duration(3000)
.attr("transform", function(d) {
var comarca_code = parseInt(d.properties.comarca, 10);
scale_factor = Math.sqrt(data_values[comarca_code-1].Density/max_density);
var centroid = path.centroid(d),
x = centroid[0],
y = centroid[1];
return "translate(" + x + "," + y + ")"
+ "scale(" + scale_factor + ")"
+ "translate(" + -x + "," + -y + ")";
});
});

d3.select("#changeActual").on("click", function() {
comarques.transition()
.duration(3000)
.attr("transform", function(d) {
var centroid = path.centroid(d),
x = centroid[0],
y = centroid[1];
return "translate(" + x + "," + y + ")"
+ "scale(" + 1 + ")"
+ "translate(" + -x + "," + -y + ")";
});
});

});

});
</script>
``````