Map with d3.js and TopoJSON, Albers Siberia projection -


i'm trying make choropleth d3.js got stucked @ beginning. found shapefile , generated geojson , topojson files here. map uses albers-siberia projection. found projection:

projection: albers equal-area conic

  • units: meters
  • spheroid: krasovsky
  • central meridian: 105
  • standard parallel 1: 52
  • standard parallel 2: 64
  • reference latitude: 0
  • false easting: 18500000
  • false northing: 0

proj.4: +proj=aea +lat_1=52 +lat_2=64 +lat_0=0 +lon_0=105 +x_0=18500000 +y_0=0 +ellps=krass +units=m +towgs84=28,-130,-95,0,0,0,0 +no_defs

mapinfo: "albers-siberia", 9, 1001, 7, 105, 0, 64, 52, 18500000, 0.

so got code , make nothing (and freez up), what's wrong?

<!doctype html> <html lang="en"> <head>     <meta charset="utf-8">     <title>choropleth</title>     <script type="text/javascript" src="d3/d3.v3.js"></script>     <script type="text/javascript" src="d3/queue.v1.min.js"></script>     <script type="text/javascript" src="d3/topojson.v0.min.js"></script> </head> <body>     <h1>my choropleth</h1>     <script type="text/javascript">          var width = 960,             height = 500;          var svg = d3.select("body").append("svg")                     .attr("width", width)                     .attr("height", height);          var pr = d3.geo.albers()             .center([105,0])             .parallels([52, 64])             .scale(1000);           var path = d3.geo.path().projection(pr);          d3.json("map_rus_topo.json", function(error, map) {          svg.append("path")           .datum(topojson.object(map, map.objects.map_rus))           .attr("d", path);         });      </script> </body>

can find json files here.
, 1 more question: how can reference value of region field in my topojson file.

the first problem geojson file isn’t in degrees [longitude°, latitude°], otherwise known epsg:4326 or wgs 84. convert geojson file wgs 84, first need create projection file, albers.prj can tell ogr source projection is.

+proj=aea +lat_1=52 +lat_2=64 +lat_0=0 +lon_0=105 +x_0=18500000 +y_0=0 +ellps=krass +units=m +towgs84=28,-130,-95,0,0,0,0 +no_defs

then, “unproject” geojson file converting wgs 84:

ogr2ogr -f geojson -s_srs albers.prj -t_srs epsg:4326 map_rus_wgs84_geo.json map_rus_geo.json

now can convert topojson in wgs 84, rather projected coordinates. i’ve taken liberty of doing simplification:

topojson -o map_rus_wgs84_topo.json -s 1e-7 -- russia=map_rus_wgs84_geo.json

the second problem projection definition in d3 incorrect. d3.geo.albers projection has default rotate , center that’s designed u.s.-centered map, in addition defining center you’ll need override default rotation. in fact, +lon_0 (central meridian) projection parameter maps projection’s rotation, not projection’s center. giving:

var projection = d3.geo.albers()     .rotate([-105, 0])     .center([-10, 65])     .parallels([52, 64])     .scale(700)     .translate([width / 2, height / 2]);

(i fudged center parameter put russia @ center of viewport. can compute automatically if prefer.) should see this:

albers siberia

it’s possible work projected (cartesian) coordinates in topojson, , define d3.geo.path null (identity) projection, i’ll leave separate question.


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