First he marked on a map the exact places where all the dead people had lived.
正确的语序是：First he marked the exact places where all the dead people had lived on a map.这里讲on a map 提前是为了强调它,翻译时的语气也有点不同,原句的翻译是：首先他在地图上标出了那些逝去的人曾经居住的确切位置.