經建版地形圖和像片基本圖在濱線繪製上的應用與限制

臺灣近一百年來累積豐富圖像資料，但因並非針對海岸環境而製作，應用於海岸濱線變遷研究時，有必要了解各式圖資及所標示之海陸界線的特性。本文以經建版地形圖、像片基本圖套色版及單色版作爲研究對象，探討應用這類圖資進行濱線繪圖(shoreline mapping)的限制與可應用性。經由疊圖分析發現，經建版地形圖水涯線常爲綜合數年標稿、編稿結果；像片基本圖套色版在不同圖幅、出版年代之水涯線的繪製時，有判定標準不同的狀況，這可能是因爲缺乏明確繪圖規範，以及繪圖者不熟悉濱線變動性的緣故。因此，爲提高各作業人員判釋濱線的一致性，未來有必要給予海岸作用和地形特徵判釋訓練。像片基本圖單色版以航照影像爲底圖，理論上，研究者可自行判釋各類濱線指標。但配合歷年航照拍攝資料及比對現場測量剖面，發現由於航照拍攝作業時，不會特別考慮潮汐、風浪等狀況，大幅增加分析和解讀濱線變遷資料的難度。綜而言之，國內圖資大多是爲了調查及經營陸地資源而生產的「陸圖」，並非針對海岸區域測量及繪圖，在使用之前，應評估既存圖資的特性，並選定適宜的濱線指標。本文也建議，政府應盡快建立以海岸監測爲目的之濱線繪圖規範，通盤考量新興影像、技術和各式既存圖資的特性，選定通用且合宜的濱線指標和作業流程，以建置可長可久的濱線變遷資料庫，並盡可能回溯和正確解讀海岸環境變遷歷程。

關鍵字

濱線繪製；濱線指標；陸圖；經建版地形圖；像片基本圖

並列摘要

For detecting historical shoreline change for Taiwan's coast, various sets of topographic maps and orthogonal maps have been adopted in previous studies. ‘Water-edge line’ shown on the maps were always regarded as the shoreline and digitized directly in these studies without questioning of which shoreline indicators they stand for. In order to understand the limitation and applicability of the topographic maps and orthogonal maps, the production of water/land boundary on these maps were discussed thoroughly. It is found that the 'water-edge line' shown in a single frame of the topographic map, is usually a product generated from various years. Identification of the water-edge line from the orthogonal maps is apparently not consistent across map-editing staffs, mainly due to the lack of understanding of dynamics in the nearshore zone. In general, abundant topographical maps and orthogonal maps in Taiwan have been produced mainly for terrestrial resource management purpose. Daily and seasonal variability of the water level is not the major concern when the plan of taking aerial photograph is made. Thus, it is essential to evaluate the source maps before conducting the process of the shoreline mapping. It is suggested that the national standard of shoreline mapping should be prepared as soon as possible.