Development of comparison support tools for historical maps using IIIF

2.1. System requirements

To support the aforementioned research, the following platform is envisioned:

• Analysis support functions combining related resources, such as modern maps, with historical maps.
• Comparison support functions for historical maps based on common place names in multiple historical maps.

In realizing these functions, useful technologies such as georeferencing and side-by-side image display using Mirador IIIF Viewer have been proposed, but the following challenges were identified:

• For the former, concerns were raised about the distortion of historical maps due to georeferencing. In response, effective methods like Maplat (Otsuka 2019), which overlays modern maps with historical maps without distortion, have been proposed. However, issues such as non-compliance with IIIF were identified.
• For the latter, while side-by-side display of multiple images using Mirador is available, manual operation is required to focus on points of interest within the historical maps for comparison.

2.2. Existing Research

There are numerous studies that support the viewing and analysis of maps and historical maps. Furthermore, many tools, such as Old Maps Online, Map Warper and Map Folder (El Khatib 2020), are also available. This study focuses on analyzing maps that are annotated with place names and comply with IIIF. Recently, methods combining IIIF with georeferencing have emerged, and tools and viewers utilizing IIIF for georeferencing, such as Georeferencer (Kowal et al. 2012) and Allmaps (Allmaps 2024), have been developed. In May 2023, the IIIF Georeference Extension (Georeference Extension 2024) was also released. This research distinguishes itself by developing analysis support tools, utilizing the existing research outcomes and considering the recent trend of employing IIIF in map and diagram analysis. 

3.1. Side-by-Side Display of Modern Maps and Historical Maps

Figure 1 shows a screen example of the viewer developed for this annotation data, which is created with Allmaps. It provides a modern map, diagram, a list of place names, and a search function. By clicking on a marker on the modern map or an annotation on the diagram, the corresponding location on the other is focused. This functionality and viewer allow the user to check the correspondence between the diagram and the modern map without distorting the diagram.

Figure 1: Side-by-Side Display of Modern Map and Historical Map

3.2. Support for Comparing Multiple Historical Maps

It is assumed that the place names within each map image being compared are annotated. Furthermore, each place name is assigned an ID, and it is assumed that the relationships between corresponding place names in different maps can be retrieved through IDs or similar means. For such data, the annotation description defined in the IIIF Presentation API has been partially extended. A field named 'cid' (common ID) was added to propose a description method that assigns a common ID to corresponding place names. Additionally, a viewer has been developed that can load manifest files with this description, search for annotations with corresponding IDs in multiple historical maps, and focus on the corresponding annotations.

Figure 2 illustrates an example where a list of place names is displayed at the center of the screen, with corresponding place names in the left and right historical maps being automatically focused.

Figure 2: Mirador Plugin for Comparing Multiple Historical Maps