- Introduction to Historical GIS and the Study of Urban History
Over the past decade or so geographic information systems (GIS) methodology has become an accepted tool in historical research (Gregory and Ell 2007; Knowles 2008). Although often regarded as a mapping tool, GIS is perhaps better thought of as a type of database. What makes a GIS database unique is that a location is stored for each item of data, with this location taking any of a variety of forms: a point, a line, a polygon representing an area or zone, or, in the case of a raster system, a pixel. GIS can then present instantly on the screen a map showing the distribution of any variable or combination of variables in any of the chosen locational formats. This electronic display of information becomes an analytic tool, allowing the refinement of research questions, with answers displayed instantly: GIS creates a display of information once visible only in paper form, drawn slowly and expensively first by cartographers and then by vector plotters. GIS and its associated tools transform mapping into a dynamic exploratory process.
The fact that the data in a GIS database are spatially referenced allows a researcher to produce maps quickly, easily, and potentially in large volumes; but a number of other advantages also make GIS a platform that is well suited to the analysis of the geographies of the past. The first is that, as all data in a GIS-informed project have an explicit spatial location, it is easy to ask questions about where features are located in relation to each other. As Anne Knowles (2000: 453) notes, the enhanced visualization component of GIS has very positive results for historians, making available “dimensions of historical reality and change that no other mode of analysis can reveal.” [End Page 455]
Second, as the locational data are based on real-world coordinate systems, such as latitude and longitude, Universal Transverse Mercator, or British National Grid, any dataset can potentially be integrated with any other dataset. Thus, for example, data on specific buildings based on points can be integrated with demographic data from census tracts represented as polygons, transport information can be represented as lines, and data on heights can be represented as pixels on a raster surface. This enables complex representations of a study area to be built up from multiple, apparently incompatible sources.
Third, and perhaps most important, GIS allows the researcher to explore the topic under study in a way that explicitly considers the impact of space and location. This might involve using formal spatial statistical methodologies (Fotheringham et al. 2000; Maguire et al. 2005) or might simply involve asking questions about why different places appear to behave in different ways. The increasingly sophisticated suite of statistical tools that accompany GIS software provide insight into the strength, rather than just the existence, of a spatial pattern, indicating how tightly grouped or widely dispersed it is. As correlation coefficients are to a scatter plot, so measures of the characteristics of spatial distributions are to the visualization of those patterns, providing indexed scores of the strength of complex relationships. Spatial statistics likely will assume increasing importance in guiding the development of GIS as this revolution turns from visualization to more ambitious analytic pursuits. At the very least, GIS enables and encourages the researcher to think carefully about the geography of the topic under study and the explanatory power of that geography.
While GIS approaches have these advantages, they also have a number of drawbacks. First, the time it takes to create a GIS database can be large, greatly increasing the variety of costs associated with a GIS-informed project. Second, the use of GIS software requires that the researcher learn certain technical skills, demanding additional time and effort. Third, and perhaps most fundamental, there is a lack of strong geographic skills among historians who are more used to asking questions about change over time. This relative neglect of the geographic tradition means that even with a good database and the technical skills to use it, a researcher still needs the conceptual tools to frame research questions and conduct the research...