render with one loop

world.js

    function drawMap(map) {
        var i, x, y, height, pos,
            width = map[0].length,
            total_nodes = map.length * width;
        for (i = 0; i < total_nodes; i++) {
            x = i % width;
            y = Math.floor(i / width);
            height = {
                top:    map[y][x],
                right:  map[y][x+1],
                bottom: map[y+1][x+1],
                left:   map[y+1][x]
            };
            pos = {
                x: x,
                y: y
            };
            drawTile(pos, height);
        }
    }