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June 2004 |
Distribution analysis of sites based on GIS
NETWORK MODELS
We introduce two types of network models to consider the relationship between nucleus villages and hill-forts [6,7,8,9]. Both models have been presented based on different purposes, respectively. They have already been implemented as key functions of FHSS, supporting the archaeological network analysis. Some of the analysis presented in this paper has been obtained by using FHSS.
Village network model of nucleus village sites
The first model, termed village network model, is defined to extract networks consisting of routes for cultural exchange between nucleus villages. Cultural exchange would take place on the basis of movement of people: Since roads were basic facilities for their movement, our village network model shows what roads or routes should exist between nucleus village sites.
In general, there are numerous possible routes to link two distant sites: a route is given by a collection of roads to link intermediate sites one after another. We guess that the main route between two distant sites should be one with the minimum cost among such possible routes as above. Here, we introduce the cost function for the movement of people as follows:
Let f(x) be the cost of movement, x be moving distance and k be a constant. Then we assume:
A general solution of this equation is given by:
Where C is a constant. exp(·) denotes the exponential function with base e. We assume C=1. Basically, the smaller the f(x), the easier it would be for people to move. k(>0) means a value which controls difficulty of movement. k has been playing an important role in determining routes. Fig. 1 presents an example detecting a route with the minimum cost between sites a and c where k=1.
Beacon telecommunication network model of hill-forts
The second model is the beacon telecommunication network model, which has been based on the hypothesis that hill-forts were equipped with beacon facilities. By using FHSS, a beacon telecommunication network between hill-forts has been detected; visibility between the sites has been verified based on the 3-dimensional terrain database. The result is approximately the same as that of a field experiment conducted by a group of archeologists as previously mentioned. Practically, our verification has been carried out by examining visibility between every pair of sites; i.e. we examine whether avers site can be seen from other sites without geographical obstacles.
The network has been defined by connecting "visibility relations" between the sites. The digital terrain data consisted of 50×50 metres blocks was provided by the Japan Geographical Survey Institute [10]. An altitude value for a block is quantized at a 10cm interval. FHSS has two parametres: visibility range h and height of stand r. Visibility range is nothing but the maximum distance at which people in a hill-fort could recognize smoke coiling up from another distant place. Height of stand means height of the smoking stand or watching stand in a hill-fort. It has been added to altitude of each hill-fort sites in the computing process of FHSS, acting to eliminate some kinds of effects in relation to the quantized altitudes of digital terrain data. Here, we omit some of the more detailed description of technical procedure to examine visibility between two sites. Fig. 2 illustrates our procedure to examine the visibility.
Fig 1 Routes and Costs
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