Help with georeferencing

klaarenbeek, reinoutDo you like old maps? Then help the University Library to georeference pre-1900 maps in its Map Collection. ‘Georeferenced maps are easier to find and better searchable for researchers and students all over the world,’ says curator Reinout Klaarenbeek. ‘It makes it possible to search geographically within map collections.’

In recent years, all pre-1900 maps in the Old Maps Collection have been digitised. ‘You can see and download these maps from our Image Database. At present, however, our maps can only be found using search terms or words that appear in the detailed map descriptions.’ 

Georeferencing allows searching using a geo-webviewer
‘Once maps have been georeferenced, you can also start searching geographically,’ Klaarenbeek explains. ‘After assigning coordinates to the historical maps, you can search collections using a map instead of keywords. Georeferenced maps can be accessed in geo-webviewers. With a geo-webviewer you can zoom in on a certain area and retrieve all the (georeferenced) maps for that area.’ VU’s Old Maps that have already been georeferenced can be viewed at VU Geoplaza. Klaarenbeek is also going to place them on other online platforms ‘so students and researchers from all over the world will be able to search different collections simultaneously.’

How does georeferencing work?
‘Georeferencing means to superimpose an old map on a recent map. We apply the cutting-edge web-application Georeferencer, accessible through Geoplaza, to help us do this. In this application, you can identify geographical locations where both the new and the old maps match. You have to identify at least five locations. The computer then calculates how to adjust the old map in order to match it to the recent map. However, the more points you identify, the more accurate the projection. It’s a bit of a puzzle.  

Accuracy of historical maps
‘Georeferencing gives us insight into how geometrically correct old maps are. In the past, cartographers had far fewer technical tools, so their maps were often less accurate. We would like to know for example how precise distances are on the old maps. Georeferenced maps also provide valuable insights into geographical changes that have taken place over time. Researchers studying urban development or landscape change often use superimposed historical maps in their work. Georeferenced maps make this kind of research much easier.’

Maps of the famous Blaeu family of cartographers of Amsterdam
‘We start with the oldest maps and work our way forward in time. Now anyone can georeference our oldest maps (1600-1800). Among them are beautiful maps from Frederik de Wit's Atlas sive Descriptio terrarum orbis (ca. 1680) and maps of the famous Amsterdam family of cartographers Blaeu.’

Works of art
‘I've been fascinated by maps ever since I was a child. Maps, especially old ones, are true works of art. Everyone is very welcome to participate in this work. You can admire all those beautiful maps and see how cities and lands have changed shape or name. At the same time, you will be helping to make the maps more accessible for educational and research purposes. There are about 3,500 maps to be georeferenced, so we are very grateful when people are willing to help.’

Keen to help us out?
On the Geoplaza website you find georeferencing instructions, see examples and find more background information about the maps and the project.