Map with German electoral districts

 

For a more elaborate version see http://vis.uell.net/wahlatlas/.

© Bundeswahlleiter, Statistisches Bundesamt, Wiesbaden 2008, Wahlkreiskarte für die Wahl zum 17. Deutschen Bundestag

Geoinformationen © Bundesamt für Kartographie und Geodäsie www.bkg.bund.de

The underlying JavaScript code

<script type="text/javascript" src="/ajax/germany.js"></script>
<div id="wahlkreis">&nbsp;</div>

var minX =-289319.4,
    maxY = 6827620,
    maxX = 351315.7,
    minY = 5960587,
    brd,
    wahlkreisNode = document.getElementById('wahlkreis').firstChild,    
    points = [],
    len = data.length, // from germany.js
    lastWk = null,
    i, col = 0;
    
brd = JXG.JSXGraph.initBoard('jxgbox', {boundingbox:[minX-1000,maxY+1000,maxX+1000,minY-1000],keepaspectratio:true});

for(i=0;i<len;i++) {
    if(i%6==1) {
        lastWk = data[i];
    }
    else if(i%6 == 5) {
        points.push([data[i],lastWk]);
    }
}

function createCurve(area)  {
    var compos = area[0].split(';'), // Connected component
        x = [], y = [],
        c = [], num, i, a, graph, k, a;
        
    num = compos.length;
    for (k=0;k<num;k++) {
        x = []; y = []; c = [];
        xy = compos[k].split(',');
        len = xy.length;
        for(i=0;i<len;i++) {
            a = xy[i].split(' ');
            c.push(new JXG.Coords(JXG.COORDS_BY_USER, [1*a[0], 1*a[1]], brd));
        }
        c = JXG.Math.Numerics.RamerDouglasPeuker(c,1.3);
        len = c.length;
        for (i=0;i<len;i++) {
            x.push(c[i].usrCoords[1]);
            y.push(c[i].usrCoords[2]);
        }
        graph = brd.create('curve', [x,y], 
                    {fillColor:JXG.hsv2rgb(0.5*(col++),0.5,0.9),
                     highlightFillColor:'yellow',
                     strokeWidth:1,strokeColor:'black',highlightStrokeColor:'black'});
        if (k==0) {
            JXG.addEvent(graph.rendNode, 'mouseover', function(){graph.nohcol = graph.visProp.fillcolor; graph.setAttribute({fillColor: 'yellow'});}, graph);
            JXG.addEvent(graph.rendNode, 'mouseout', function(){graph.setAttribute({fillColor: graph.nohcol});}, graph);
        }
        graph.hasPoint = function(){return false; };
    }
}

brd.suspendUpdate();
JXG.timedChunk(points, createCurve, null, final);