Geographical Information Systems (History)
To find a remarkable implementation of a system that uses GIS as one of the component parts of its technology, one need look no further than Google Earth to illustrate an essential facet of what it is possible to do using such techniques. Satellite imagery of actual terrain can be overlaid with a wide variety of information choices including transportation, roads, shopping and services information and even user generated information about very specific buildings or neighbourhoods. Obviously, the type of technology that Google has the capability to implement has global significance and requires an extraordinary amount of computational and storage capacity, but nonetheless, the layered approach to information is the same principle that arts and humanities academics (principally perhaps archaeologists) have used for many years when applying GIS principles to research.
The basic unit of representation in a GIS system is the layer, which has information associated with it to describe what that layer represents. Spatial data refers to the actual point on the earth’s surface that the point or boundaries of the layer refer to and this is described using either latitude and longitude readings or other co-ordinate systems such as the British National Grid or the Universal Transverse Mercator (UTM). The boundaries of the layer for this purpose can be defined as either a point, a line, a polygon, or a pixel, and each of these is represented using co-ordinate pairs. Attribute data constitutes the information that is associated with the spatial data and might consist of any information, but is generally text or statistics or graphical representations of data that is relevant to that location. The industry standard package is the ArcGIS suite of tools which incorporates ArcView and ArcInfo, widely used by academic and commercial project teams, but a range of other products are available, including a freeware system called GRASS (Geographic Resource Analysis Support System).
It is clear then that GIS has enormous value for the annotation of maps, but it is has perhaps been less clear to historians over the years how a temporal component can be introduced to the system that will allow the description of changes over time. At a recent Methods Network Expert Seminar, Ian Gregory gave a presentation that referred to problems of ‘time’ and ‘space’ and did so in the context of talking about infant mortality trends in England and Wales from the 1850’s to the 1900’s. A temporal component to his research was provided by the Great Britain Historical GIS (GBHGIS, Gregory et al 2002), hosted at the University of Portsmouth, which provides: census reports; data on births, marriages and deaths; and on unemployment and poor law statistics, for the entire period of Gregory’s study. The present incarnation of this system (in development since 2001) has provided scholars with a new resource in this particular area of research, and has also been the data source for a major lottery-funded project of wider immediate benefit to the public, the Vision of Britain website. (http://www.visionofbritain.org.uk/index.jsp) By overlaying statistical representations of infant mortality figures onto precise areas, it is possible to graphically display - in much more detail than was possible before - changes throughout the period and how they relate to a number of factors, notably the difference in death rates throughout urban and rural areas.
A similar initiative, also launched in 2001 is the China Historical GIS, hosted at Harvard, which features historical maps and datasets that are freely available for academic use. (See Fig. 5)
The use of GIS as a ‘hub’ technology around which an archive can be built is described in the AHDS Guide to Good Practice: A Place in History: a guide to using GIS in historical Research. It quotes an example from the Perseus Digital Library, which features the Edwin C. Bolles Collection of the History of London. This includes maps of London from different periods presented as different layers, over which place names can be compared and references made to source texts.
Returning to a project mentioned elsewhere in this wiki, the ‘Valley of the Shadow’, GIS is also a component of the functionality of this project and over 2000 individual dwelling places, taken from a very detailed map of Augusta County, Virginia (1870), are precisely pinpointed for the purposes of allowing users of the system to be able to identify the houses of particular individuals featured elsewhere on the site.