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8.2 Types of qualitative data in GIS Many qualitative projects follow a data-led approach. Often a large amount of disparate information about a place or places is gathered and integrated using the locational characteristics of the data. By assembling the data in this way it becomes possible to explore them to form new insights. Qualitative information is often point-based, but can also involve lines or polygons. Examples of the types of qualitative attribute data that may be used in GIS include information on the presence or absence of features such as roads and buildings, documents concerning events that occurred at a place, pictures or photographs relating to places, or audio or video that refer to a specific location. Textual descriptions of places from historical manuscripts can also provide data for a qualitative GIS. Historical maps or plans could also be part of the qualitative attribute data, particularly if they have relevance to an area but cannot be geo-referenced in the manner of modern-style maps. Rather than store all the information about a place in a single GIS, the GIS attribute data could consist of hyperlinks to websites that contain information about specific places or themes. All that is required to turn these into GIS data is a coordinate-based location. Traditionally, the locational component of qualitative information is less likely to fit the precisely defined locations insisted on by GIS software. In some ways, this is less of a problem than it can be for quantitative data because the types of analyses that are performed are less likely to be as demanding of the spatial component than, for example, areal interpolation operations using quantitative data. In spite of this, the accuracy of the locational data, particularly data derived from different sources, still needs to be carefully considered. The use of qualitative sources to date often represents a more sophisticated use of the metadata (see Chapter 9) about an object. For example, the catalogue for a collection of scanned photographs is likely to have included some information about the place that the photographs refer to, usually place names. By converting these place names into spatial data, probably points, we have the ability to create a layer of scanned photographs. As with other GIS applications, this allows us both to find more information about the collection of photographs themselves, for instance, by comparing images of locations that are near to each other; and it also allows us to integrate the collection of photographs with other collections of photographs or perhaps with other types of information. |
