A place in history: a guide to using GIS in historical research

CHAPTER 1: GIS AND ITS USES IN HISTORICAL RESEARCH

1.2 The terminology of GIS

An examination of the basic GIS texts will give many different definitions for GIS. The reason for this is that there are two basic ways of approaching GIS. It may be regarded from a tools-orientated point of view that explores how the software models the world; or from an approach-orientated point of view that explores what GIS allows us to do.

The tools-oriented approach describes GIS from the point of view of the software, for example, ArcView or MapInfo. These are often regarded as complex computer mapping programs. This is a misapprehension: GIS software combines computer mapping functionality with a form of database management system (DBMS) such as Dbase, Microsoft Access, or Oracle. Computer mapping systems such as Adobe Illustrator or CorelDraw are designed to produce high-quality graphical output. They include functionality such as the ability to draw features, move features from one location to another, change shading and line width, and so on. Although some, but by no means all, of this functionality will be found in GIS software, it is more helpful to think of GIS as a spatially-referenced database. As such, the data are represented in two ways. Firstly, there are rows of data found structured in the same way as in a conventional database. In GIS terminology this is called attribute data. Many GIS software packages allow attribute data to be stored in conventional database management systems such as the ones described above. The special feature of GIS software is that each row of attribute data is also represented by a spatial feature that is represented by coordinates and is thus mappable. This spatial feature will be a point, a line, a polygon (the technical term for an area or zone) or a pixel depending on the type of data it is representing. This is termed the spatial data. Using this combination of attribute and spatial data GIS data combine information on what an object is with information on where it is located for each feature in the database.

Figure 1.1: The basic structure of GIS
There are two components: spatial data that show where the feature is; and attribute data that provide information about the feature. These are linked by the software. In this example we have some fictional hospital data showing the location of hospitals combined with information on their names, numbers of patients and numbers of deaths

The fact that there are both spatial and attribute data allows the database to be exploited in more ways than a conventional database allows, as GIS provides all the functionality of the DBMS and adds spatial functionality. For example, a user has a conventional database consisting of data on hospitals. The columns in this database include the name of the hospital and the numbers of patients, deaths, and so on. There is one row of data for each hospital: in the GIS this becomes the attribute data. The spatial data are a point location for each hospital stored as a coordinate pair but represented on screen using a dot or another form of point symbol. The basic structure of this is shown in Figure 1.1. This combined representation of the study area opens up a whole new range of possibilities that neither a DBMS nor a computer mapping system could handle on their own: for example, we could draw the locations of all the hospitals, click on one of them, and have the system list its name and other attribute data. We could also select only the hospitals with, for example, over 1,000 patients. In a conventional database all we can do with this information is list the data for the hospitals concerned. In a GIS we can do this, but we can also draw where they are, or perhaps draw all of the hospitals using different shadings to indicate their different sizes. Unlike a conventional DBMS, therefore, GIS allows users to gain an understanding of the geography of the phenomenon they are studying. Unlike a computer mapping system, GIS provides the underlying data that form the patterns shown on the map.

The above approach demonstrates that GIS software can be regarded as a spatially-referenced database. It is able to map the data and also to query it spatially, asking questions such as 'what is at this location?' that a conventional database would be unable to answer. An approach-orientated definition asks how we can make best use of this dual-component data model. This involves considering both the benefits and the drawbacks of including location into our exploration of patterns. In the GIS literature this approach has become known as Geographical Information Science (GISc), and Siebert (Siebert 2000) refers to 'spatial history' in very much the same way. This approach uses GIS as part of the process of exploring change geographically and temporally. 'Historical GIS' is also a term that is becoming increasingly used to describe approaches to historical research involving the use of GIS (Knowles 2000).

One other term that also needs defining in this section is the word space. Among the GIS community this term is used in a very similar way to the term location. Spatial data are data that refer to locations, and where a GIS book might say 'consider the role of space', a historian may well say 'consider the role of location'. There is, in fact, a slight difference in definition as space is a scientific way of defining location, usually through a coordinate system, thus 'a location in space' usually means a location that can be defined using one or more coordinates.