url_spec = cors_proxy + url_base + "/export?bbox=" + xmin + "," + ymin + "," + xmax + "," + ymax + "bboxSR=" + sr + "," + "imageSR=" + sr +"&layers=show:" + "0" + "size=" + img_width + "," + img_height +"&format=" + "png" + "&transparent=true&dpi=&f=pjson"