Why georeference historical maps?

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Georeferencing early maps is becoming steadily easier and cheaper, and provides several new ways of using and understanding maps. By Georeferencing maps, you can visualise and compare maps in new ways, improve retrieval and indexing methods, further their use, and develop different means of understanding and interpreting them.

The Georeferencer application offers a new, easy and enjoyable way to georeference historical maps, so that they can be displayed as an overlay in Google Earth and the Google Earth browser plug-in.

There is also a DLib paper about Georeferencer covering this subject: Georeferencer: Crowdsourced Georeferencing for Map Library Collections, Volume 18, Number 11/12, November/December 2012

The Wikipedia definition of Georeferencing summarises the main purposes of georeferencing and the methods involved. C. Balletti's 'Georeference in the analysis of the geometric content of early maps' is also a helpful introduction.

There are several advantages of georeferencing historical maps:

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Why be cautious about georeferencing historical maps?

There are some important methodological and practical reservations about the value of georeferencing historical maps:

  1. Georeferencing misrepresents and distorts maps by explicitly transforming or warping them. These historical maps were not intended to be changed and viewed in this way. As such, it can misuse or misinterpret historic maps, visualising them in ways that their makers and users would probably never have intended, and lead to false ideas and assumptions about the maps themselves. Georeferencing does not necessarily improve a historical map or make it more accurate. In the course of transforming the original map, georeferencing changes lines and shapes, the distances between objects, the map's aesthetics and its value as a cultural object.
  2. The georeferencing process overemphasises geometric accuracy or inaccuracy of historic maps and therefore downplays all other aspects of their content - their symbolism, placenames, the way they represent features, their purpose and usage, ideology, political and cultural role and bias, and other meanings. Taken on its own, georeferencing can therefore reinforce a positivist, modern and simplistic concept that the history of mapping is simply a history of improvements in accuracy over time, ending up with present day maps that are best of all, as well as the misconception that more accurate maps are 'better' maps. Both of these ideas have rightly been discredited.

Some of these issues were usefully discussed on MapHist in March 2009. Whilst they are important reservations, georeferencing arguably still has a role for particular maps in particular circumstances, provided these reservations are borne in mind. What may be useful and appropriate for certain 19th or 20th century maps may not be useful or appropriate for 16th or 17th century maps. The AHDS Guide to Using GIS in Historical Research has good further information about using georeferenced maps and other information in historical applications. The NLS Map images website shows all maps first and foremost in their authentic, original state as ungeoreferenced images. The Georeferencer application allows ways of creating and viewing georeferenced versions as an added extra, only for those who wish to explore this technique and visualise the maps in this different way.

This is only a brief look at this topic and we would be interested to hear your views. Please e-mail geo@nls.uk to provide general comments/feedback.