歴史的地図リテラシー促進のための動的局所ジオリファレンシングWebプラットフォームの開発と応用

抄録

Historic maps are not merely records of past geospatial information; they also mirror the social, cultural, and technological contexts of their era. Because these maps often feature deliberate distortions, stylized perspectives, and selective details, understanding them requires advanced map literacy—a skill set that includes recognizing cartographic biases, contextual intentions, and the expressive artistry behind historical representations. However, conventional georeferencing methods—which typically apply a single global transformation—can diminish the uniqueness of bird’s-eye-view or pictorial maps by forcibly “correcting” local variances in scale and orientation. This undermines the very features that make historic maps valuable resources for cultivating deeper spatial awareness and interpretation skills.

In response to these challenges, we propose Dynamic Local Georeferencing (DLGR), an approach designed to preserve and highlight mapmakers’ intentions while aligning historic maps with modern coordinate systems. DLGR subdivides a historic map into small triangular regions using a Triangulated Irregular Network (TIN), then applies local affine transformations to each region. This allows for area-specific alignment that more accurately captures each map’s inherent distortions.

To facilitate both practical use and the development of map literacy, we developed a web platform called DLGR Mapper. One of DLGR Mapper’s key features is its ability to maintain the original integrity of historic maps while allowing users to easily identify corresponding points, lines, and areas with modern web maps and other historic maps. By enabling users to interactively place and adjust control points, DLGR Mapper transforms georeferencing into a hands-on exploration of cartographic design choices. Through real-time visualization of how the map reshapes, users gain a critical understanding of how historic maps were drawn, what they sought to emphasize, and why certain distortions were introduced. Case studies of Yoshida Hatsusaburo’s 1936 bird’s-eye-view map of Akita City and multiple historic maps of the former Kakunodate Town and Araya Town illustrate how DLGR Mapper reveals the layered narratives embedded in cartographic artifacts.

By turning georeferencing into an interpretive learning process, DLGR can contribute to fostering heightened map literacy and encouraging deeper engagement with the cultural and historical dimensions of cartography. Furthermore, DLGR can support users in performing spatial reasoning directly on historic maps, enhancing their ability to critically analyze geographic relationships and the historical narratives embedded in cartographic representations. Finally, future developments may involve integrating more flexible transformation models, 3D spatial data, and AI-driven control-point identification to further enhance the tool’s accuracy, usability, and educational impact in advancing historical map literacy.

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