refactor(es modules): split layers to modules

src/layers/renderers/drawPopulation.js

@@ -0,0 +1,41 @@
+export function drawPopulation(event) {
+  population.selectAll("line").remove();
+
+  const {cells, burgs} = pack;
+  const p = {cells};
+  const show = d3.transition().duration(2000).ease(d3.easeSinIn);
+
+  const rural = Array.from(
+    cells.i.filter(i => cells.pop[i] > 0),
+    i => [p[i][0], p[i][1], p[i][1] - cells.pop[i] / 8]
+  );
+
+  population
+    .select("#rural")
+    .selectAll("line")
+    .data(rural)
+    .enter()
+    .append("line")
+    .attr("x1", d => d[0])
+    .attr("y1", d => d[1])
+    .attr("x2", d => d[0])
+    .attr("y2", d => d[1])
+    .transition(show)
+    .attr("y2", d => d[2]);
+
+  const urban = burgs.filter(b => b.i && !b.removed).map(b => [b.x, b.y, b.y - (b.population / 8) * urbanization]);
+
+  population
+    .select("#urban")
+    .selectAll("line")
+    .data(urban)
+    .enter()
+    .append("line")
+    .attr("x1", d => d[0])
+    .attr("y1", d => d[1])
+    .attr("x2", d => d[0])
+    .attr("y2", d => d[1])
+    .transition(show)
+    .delay(500)
+    .attr("y2", d => d[2]);
+}