波特兰海图研究及存在问题的分析

The Research on Portolan Charts and Analyses of Its Issues

13-18世纪,波特兰海图作为一种航海必备工具,在西方海图史上占有重要地位。波特兰海图的特征包括图上呈放射状的网格线及表示16或32个方位的风玫瑰或罗盘玫瑰,早期绘制范围基本围绕地中海和黑海地区,部分涉及从丹麦到摩洛哥的大西洋以及不列颠岛海岸,地理大发现之后随着殖民者的足迹扩大到全世界。此外,沿海地名均垂直于海岸线标注,部分海图上可见距离比例尺。15世纪末,波特兰海图上开始出现纬度标注,17世纪出现经度标注。早期海图外观上存在意大利式简洁朴素与加泰罗尼亚式精美繁复两类不同的绘制风格,学界普遍认为前者的航海实用性更高。具体使用过程中,波特兰海图与罗盘定向、浮标测速、Toleta表修正航道,一起构成了航位估算法的使用基础。波特兰海图经西方学者百余年的研究,成果颇丰,但围绕其起源与实用性两大主题的论争却一直存在,其与磁罗盘之间的关系也一直难以厘清,其在具体航海过程中的使用究竟如何等问题仍悬而未决。

As an essential navigational tool,the portolan charts played an important role in the history of marine cartography of the western world from the 13 th to the 18 th century. The portolan charts were characterized by distinct wind rose or compass rose with 16 or 32 bearings and loxodromes or rhumb lines which were equidistant compass points in a large circle with straight lines running between each and beyond to the edge of the vellum. The geographical scope on early portolan charts usually covered the area of Mediterranean and Black seas,some extending to the Atlantic coasts from Denmark to Morocco and that of the British Isles,and finally covered the entire world after the age of the geographic discovery. In addition,place names were marked perpendicularly to the coastline and there was legend of distance scale on some charts. Latitude scale began to appear on portolan charts in the late 15 th century while longitude scale appeared later in the17 th century. There were two different charting styles. One was the simple Italian style and the other was the over-decorative Catalan style. Scholars agree that the former was more practical for navigation. The simultaneous application of magnetic compass,chip log and Toleta with portolan charts constituted the basis for Dead Reckoning. Although the western scholars have studied portolan charts for more than a hundred years and made great achievements,they failed to reach an agreement on the origins and applicability of the charts. Other issues such as the relationship between the chart and the compass,and the role the chart plays during the navigation are still pending and need further research.