function roll_over_map(img_name, img_src) {
    document[img_name].src = img_src;
}
function popup_over_map(img_name, img_src_before, img_src_after, popup_name, popup_option) {
    document[img_name].src = img_src_before;
    window.open(popup_name,'popup',popup_option);
    document[img_name].src = img_src_after;
}