地形圖中子午線收斂角表示法之研究

子午線收斂角係指方格北與真北間的夾角，當地圖經由指北針法標定地圖方位，即可按子午線收斂角測出真北方向。目前我國出版的各比例尺地形圖中，子午線收斂角係在偏角圖中標註，並以圖幅平均子午線收斂角的方式表示。但平均值僅相當於圖幅中央位置，對用圖者仍無法了解整張圖幅子午線收斂角大小之分布。基此，本文將探討平均子午線收斂角之精度表示，並進一步求解不同比例尺地形圖中之相應精度。此外，在橫麥卡托投影結構下之地形圖，從早期6°分帶到目前採用2°分帶製圖，對子午線收斂角嚴密公式之解析，進而提出實用公式，將有助於我國地形圖的編製作業。

關鍵字

子午線收斂角；方格北；偏角圖；地形圖；橫麥卡托投影

並列摘要

A meridian convergence is the angular difference between grid north and true north. Therefore the true north can be determined by putting a compass on a map with the indication of the meridian convergence showed as a mean value. Currently, in all varieties of topographic maps published in Taiwan, the meridian convergence, generally referred as a mean value, is marked on the declination diagram. The mean value of the meridian convergence could be located in the middle part of the map but map user could not be able to figure out the distribution of its varieties in the whole map. Hence, in this paper the accuracy of the mean value is analyzed and manipulated to derive the relative accuracy in different scales of topographic maps using transverse Mercator projection. Besides, from 6° to 2° zone mapping the detailed strict equation is analyzed and its practical equation proposed. It is concerned that this research is contributive to the topographic map compilation.