def edge_to_GeoJSON(edge, graph, color="#F5A207"):
    """Convert edge to GeoJSON string."""
    start = edge[0]
    end = edge[1]
    start_lon = graph.nodes[start]['lon']
    start_lat = graph.nodes[start]['lat']
    end_lon = graph.nodes[end]['lon']
    end_lat = graph.nodes[end]['lat']
    edge_string = ''
    edge_string += '{ "type" : "Feature",\n'
    edge_string += '"geometry" : {"type": "LineString", ' 
    edge_string += '"coordinates": [[%f,%f], [%f,%f]]},\n'%(
        start_lon, start_lat, end_lon, end_lat)
    edge_string += '"properties": {"marker-color": "%s"}\n'%(color)
    edge_string += '}\n'
    return edge_string