圖像資料在臺灣地區地形變遷研究上的應用與限制

Abstract

地形變化的訊息具有空間性，圖像資料(pictorial materials)是最能有效展現這類訊息的素材。各種圖像資料的可用性，主要取決於地形本身的特性，以及圖像資料的製作品質、比例尺、註記相關地形特徵之原則與多寡、和保存現狀。本文之目的在於以本島河道、海岸、坡地三類地形的變遷為例，說明各式地圖和航空照片中所提供的地形訊息與使用上的限制。就筆者所知，目前在臺灣地區可以獲得的最早可用作地形變遷之定性和定量研究的地圖和航空照片，應該是1904年出版的臺灣堡圖和1950年前後拍攝的航空照片。近年來拍攝之高精度衛星影像是很有用的材料，但能回溯之年代有限。清代出版之地圖精確度較低，大多只適合作定性分析，若能仔細推敲其他各式歷史文獻中所蘊含之對當時代環境的描寫，對還原地景將有實質的助益。若所做研究欲求取地形變化量，則研究者需要確定圖像資料的誤差必須遠小於真正的地形變化量，否則所得結果將無意義。

Pictorial materials are very useful on detecting information regarding geomorphic change since the spatial distribution of phenomena of interest is usually the best exhibited in comparison with other types of materials. The usability of various pictorial materials is mainly determined by characteristics of the landforms of interest, the purpose of the research and the quality and current condition of the materials, e.g., accuracy and precision, scale, damaging condition of materials due to shrinkage, folding, and distortion. The main aim of the paper is to introduce various types of pictorial materials available and their application and limitation on geomorphic changes. The application and the limitation of topographical maps and aerial photographs on geomorphic changes, in particular, are evaluated through the selected examples of river channels, coast, and slopes in Taiwan. Generally speaking, the maps published in 1904 and the aerial photographs taken around 1950 are the earliest available versions appropriate for detecting certain geomorphic changes in Taiwan qualitatively and quantitatively. When the quantitative inquiry is sought, it is important to be certain that the error involved is much lower than the amount of change in reality.