This well-known map is a precise representation of the stations (points or nodes) and the routes (arcs or lines) between them, yet provides only a very approximate indication of their relative locations and no indication of distances between them. A good illustration of a topological map is that of the London Underground metro system. Topology, derived from geometrical mathematics, is concerned with order, contiguity and relative position rather than with actual linear dimensions. In dealing with vector data an important concept is that of topology. Cottam Project geophysics data displayed as a raster background and overlaid with an aerial photograph interpretation (blue line data), coins (red point data), and metal artefacts (black point data). ![]() Attribute data pertaining to the individual spatial features is maintained in an external database. These can be discrete, taking the form of points (POINT or NODE data) linked together to form discrete sections of line (ARC or LINE data) linked together to form closed boundaries encompassing an area (AREA or POLYGON data). In the vector model, the spatial locations of features are defined on the basis of co-ordinate pairs. As a direct result, the issues we will be discussing here are concerned solely with the integration, management, analysis and archiving of representations of 2/2.5-dimensional space. The latter are a result of the inability of currently available analysis and display tools to adequately deal with truly 3-dimensional data. It should be noted that, to date, the principal applications of GIS within archaeology have been restricted to 2-dimensional models, and at best 2.5 dimensional representations. They differ in how they conceptualise, store and represent the spatial locations of objects. There are two principal GIS data-models in widespread use, which are termed vector and raster. Throughout, the emphasis is upon the importance of carefully recording information about the various data themes. This concentrates on generic concerns such as projections, precision, accuracy and scale and is followed by a consideration of more source-specific issues. It comprises a short review of the particular issues that relate to obtaining and integrating spatial data within the GIS database. The first half of this section highlights the most important issues that need to be considered in incorporating common sources of spatial data within a GIS database. In archaeology we routinely deal with an enormous amount of spatial data, varying in scale from the relative locations of archaeological sites upon a continental landmass down to the positions of individual artefacts within an excavated context. ![]() In effect any information concerning the location, shape of, and relationships among, geographic features (Walker 1993 DeMers 1997). Spatial data can be most simply defined as information that describes the distribution of things upon the surface of the earth.
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