Work at Queen’s University Belfast on creating the project’s digital map of Chester is now close to completion. The map layers that make up the Geographical Information System (GIS) are shown by the ‘screen-dump’ below, with particular mapped features represented by separate colours on the map and listed in the ‘window’ on the left-hand side. These map ‘layers’ collectively form the digital map of Chester’s urban landscape, as it looked c.1500, and through the GIS each of the layers is made interactive so that features of different types can be selected and shown either on their own or by being overlaid onto other chosen features. By turning off or on selected layers means that the digital map can quickly and easily be used to compare, say, the city’s medieval street patterns with its parish topography; or the areas of Chester’s ecclesiastical precincts with the locations and positions of its religious houses, churches and chapels. It is also easy to zoom in and out of the map using the toolbar, as well as to query selected features and so draw out information held on the spatial database that connects with the digital map.
Chester GIS screen dump
In digitizing these features – the process that lies behind creating these separate map layers – some difficulties and problems were of course encountered. The primary source for the map-digitizing is the Ordnance Survey 1850s 1:500 plans of the city, usefully already scanned from Chester Archives copies by Peter Davenport of The Digital Mapper. The high degree of cartographic accuracy of these OS plans is attested by how well they geo-rectified to survey control points (GCPs) gathered in Chester by the Queen’s team in September 2008, at the project’s start, using a Differential Global Positioning System (dGPS). But although accurate, using the information shown by these plans to recreate a map of Chester of c.1500 relies on the topographical survival of urban features across a period of more than three centuries.
Setting up the dGPS base station
While certain features, such as the pattern of streets, the locations of churches, and the alignment of the city wall, have largely survived in place in the urban landscape over this long interval, others have not, particularly the precincts of religious houses, and the city’s parochial topography. For these and other ‘lost’ features of the late-medieval townscape the research of archaeologists and local historians in Chester has proved invaluable, and thanks to their efforts it is possible to map, with a reasonable degree of certainty, even those long-vanished features of the late medieval city. Chester’s early historic plans also proved useful in this regard, though they generally did not geo-rectify particularly well against modern mapping, making digitization from them rather more problematic. One of these early maps that did rectify rather well is the plan of the city by Lavaux of 1745, and so this, along with the OS 1850s plans of the city, will feature in the final online map resource as one of our viewable and interactive layers.
The next stage of the process is to start linking our GIS-based digital map to the textual ‘mappings’ of the city, and connecting the mapped urban features to Chester’s local topography as described by the project’s medieval texts. That work is ongoing, and will present yet further challenges – both technical and conceptual. Meeting and addressing such challenges are of course the reason for doing this research in the first place!
