function getPath(poly) {
    var points = poly.getAttribute("points").trim().split(" ");

    if (points.length < 6) throw "degenerate polygon";
    if (points.length % 2 !== 0) throw "odd number of points";

    var d = "M " + points[0] + " " + points[1];

    for (var i = 1; i < (points.length / 2); ++i)
    {
        d = d + " L " + points[i*2] + " " + points[i*2+1];
    }

    return d + " Z";
}

function joinPolys() {

    var ps = document.querySelectorAll("polygon");

    for (var i = 0; i < ps.length; ++i)
    {
        var poly = ps[i];
        var style = poly.getAttribute("style");

        var path = document.createElementNS("http://www.w3.org/2000/svg", "path");

        path.setAttribute("style", style);
        poly.parentNode.insertBefore(path, poly);
        
        var d = getPath(poly);
        poly.parentNode.removeChild(poly);

        for (var j = i + 1; j < ps.length; ++j)
        {
            var nextPoly = ps[j];

            if (nextPoly.getAttribute("style") !== style) break;

            d = d + " " + getPath(nextPoly);
            nextPoly.parentNode.removeChild(nextPoly);
        }

        path.setAttribute("d", d);

        i = j - 1;
    }
}

joinPolys();