Using the code in http://bl.ocks.org/mbostock/4090848 plot a red circle on DC
Step 1. Change
d3.json("/mbostock/raw/4090846/us.json", function(error, us) {
to
d3.json("https://gist.githubusercontent.com/mbostock/4090846/raw/us.json", function(error, us) {
Step 2. Add the following
var loc = projection([-77.0164, 38.9047]);
svg.append("circle")
.attr("cx", loc[0])
.attr("cy", loc[1])
.attr("r", 10)
.style("fill", "red");
| <!DOCTYPE html> | |
| <meta charset="utf-8"> | |
| <style> | |
| .land { | |
| fill: #222; | |
| } | |
| .county-boundary { | |
| fill: none; | |
| stroke: #fff; | |
| stroke-width: .5px; | |
| } | |
| .state-boundary { | |
| fill: none; | |
| stroke: #fff; | |
| } | |
| </style> | |
| <body> | |
| <script src="//d3js.org/d3.v3.min.js"></script> | |
| <script src="//d3js.org/topojson.v1.min.js"></script> | |
| <script> | |
| var width = 960, | |
| height = 500; | |
| var projection = d3.geo.albersUsa() | |
| .scale(1000) | |
| .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.json("https://gist.githubusercontent.com/mbostock/4090846/raw/us.json", function(error, us) { | |
| if (error) throw error; | |
| svg.insert("path", ".graticule") | |
| .datum(topojson.feature(us, us.objects.land)) | |
| .attr("class", "land") | |
| .attr("d", path); | |
| svg.insert("path", ".graticule") | |
| .datum(topojson.mesh(us, us.objects.counties, function(a, b) { return a !== b && !(a.id / 1000 ^ b.id / 1000); })) | |
| .attr("class", "county-boundary") | |
| .attr("d", path); | |
| svg.insert("path", ".graticule") | |
| .datum(topojson.mesh(us, us.objects.states, function(a, b) { return a !== b; })) | |
| .attr("class", "state-boundary") | |
| .attr("d", path); | |
| var loc = projection([-77.0164, 38.9047]); | |
| svg.append("circle") | |
| .attr("cx", loc[0]) | |
| .attr("cy", loc[1]) | |
| .attr("r", 10) | |
| .style("fill", "red"); | |
| }); | |
| d3.select(self.frameElement).style("height", height + "px"); | |
| </script> |