The Cliometrics of Cartography: A Digital Method to Georeference and Assess the Accuracy of Historical Maritime Maps

The Institute of Economics will hold a seminar meeting as part of its Seminar Series on Tuesday, June 27, 2023: Giovanni Pala from University of Oxford will present the paper "The Cliometrics of Cartography: A Digital Method to Georeference and Assess the Accuracy of Historical Maritime Maps".

Abstract:

Maps were a key technology in modern navigation yet, until recently, the quantitative study of historical map’s content on a large scale has been limited by constraints on access to materials and by computational and technological limitations. Consequently, existing historical studies dealing with cartography have relied on representative examples and curated comparisons, without engaging in formal large-scale investigations. The recent flourishing of new digital technologies and materials encourages different approaches. In line with recent applications, this contribution presents a new digital method to automatically georeference and register changes in historical maritime cartography.

Currently, georeferencing is almost invariably done “by hand”, with the user imputing specific control points on digital raster images. The control points are associated with the equivalent points of known coordinates on the globe. Existing algorithms can then, with increasing accuracy as the points increase in number, create a georeferenced raster that is readable by a GIS software. This process, however, can be very time consuming.

The approach proposed in this contribution, by using a multi-step method that combines deep learning techniques and image analysis, automates the procedure, with promising results, and, leveraging the statistical flexibility of deep neural networks, can work on maps characterised by heterogeneous styles. The procedure offers a rapid path to geographically position families of map scans for further analysis.

An example of the type of historical analysis supported by this procedure is carried by using a segmentation network and error metric to characterise the accuracy of each map. This is determined by proxy, using the distance of 21st century coastlines from their historical equivalent as reported on the digital map scans. In this way, a dataset can be constructed that compares maps across regions and producers. They are comparable through a constant framework enabled by the fact that, since the 17th century, longitude and latitude information and standards were firmly established in mapmaking. One of the benefits of such an approach, is the construction of a repeatable assessment of maps as seen in their technological dimension, defined here as the quality of their spatial information. Accuracy is then a way of assessing the “performance” of a map design, its technical quality.

A test dataset and analysis obtained with the technique is presented for Europe during the years 1650 to 1800 AD ca. and compared with an important historical textual source providing the geolocation of important points of interest from the same time period. The resulting trends in error match remarkably.

Our approach offers insights into the methodological challenges around digitisation, as well as the rewards and malleability digitisation affords. It is also an example of how established and diffused sources can be connected and studied in new ways, giving them new life.

The Seminar will be held in Aula 6.

For online partecipation, please use this link.