Georeferencer: Crowdsourced Georeferencing for Map Library Collections

Georeferencing of historical maps offers a number of important advantages for libraries: improved retrieval and user interfaces, better understanding of maps, and comparison/overlay with other maps and spatial data. Until recently, georeferencing has involved various relatively time-consuming and costly processes using conventional geographic information system software, and has been infrequently employed by map libraries. The Georeferencer application is a collaborative online project allowing crowdsourced georeferencing of map images. It builds upon a number of related technologies that use existing zoomable images from library web servers. Following a brief review of other approaches and georeferencing software, we describe Georeferencer through its five separate implementations to date: the Moravian Library (Brno), the Nationaal Archief (The Hague), the National Library of Scotland (Edinburgh), the British Library (London), and the Institut Cartografic de Catalunya (Barcelona). The key success factors behind crowdsourcing georeferencing are presented. We then describe future developments and improvements to the Georeferencer technology.