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

CHAPTER 3: ACQUIRING SPATIAL DATA

3.1 Introduction

There is no cheap and easy way of getting spatial data into a GIS. In many cases the data capture phase of a GIS-based project is the longest and most expensive of all phases. Bernhardsen (Bernhardsen 1999) suggests that the collection and maintenance of data accounts for 60 to 80% of the total cost, in terms of both money and time, of a fully operational GIS. Other authors give higher figures. Siebert (Siebert 2000), for example, gives an honest account of the time taken and problems encountered building his historical GIS for Tokyo.

There are two basic sources of spatial data: primary sources where the data can be captured directly into the GIS, for example through the use of Global Positioning Systems (GPS); or remote sensing from satellites. More common for historians are secondary sources capture, where data from paper maps are converted into digital form. There are two ways of doing this: scanning the maps to produce raster data; or digitising the maps where points or line features are traced either directly from paper maps or from scanned images of the maps. This produces vector data. It is worth noting that the GIS definitions of primary and secondary data sources are different from the definitions used by historians. From a GIS perspective primary data are data captured directly from the real world, while secondary data are captured from abstracted sources such as maps. A map produced in the 1850s is a primary source from a historical point of view, but a secondary source from a GIS perspective.

An alternative to capturing data yourself is to acquire digital data from someone else. This is less time consuming and less risky but spatial data are often expensive, may have serious copyright restrictions placed on their use, and need to be fit for the purpose that you require. In the context of historical research, many datasets that may be required have not been digitised due to a lack of demand for them, so there is frequently no alternative but to capture them yourself.

The first and probably most important decision to take when acquiring digital spatial data is what the source should be, and this applies whether the data are to be captured in-house or acquired from others. The limitations of the original source inherently limit any subsequent use of those data. The scale of the source is of particular importance here. In general, larger scale data are more flexible than smaller scale but will be more expensive, either in terms of purchase price or the time taken to capture them, and will have more redundant information which can lead to problems with file sizes. A second issue to consider is whether the purpose the original maps were produced for makes them suitable for the types of use that the digital representation is required for.