2.5 Other systems: terrain modelling with TINs A triangular irregular network (TIN) can be created from data that, in addition to x and y coordinate values, also have a z value that usually represents altitude. Spot-heights are the most common source of data in this form. The first stage in generating a TIN is to plot all the x, y coordinates as points. Next a straight line is drawn between each point and its nearest neighbours. This is shown in Figure 2.5. As the heights of all the points are known the gradient of the line of these lines are also known. If data are available from enough points this can be used to generate a surprisingly realistic, apparently three dimensional, representation of the shape of the landscape, known as a digital terrain model (DTM). Often raster and vector data are draped over the DTM to provide features on the landscape. Models such as these are often shown on news programs, for example, the siege of Sarajevo was regularly pictured this way. 
Figure 2.5: A Triangulated Irregular Network (TIN)
From a series of points such as spot-heights, non-intersecting lines are drawn to the points' nearest neighbours. Using the 'heights' the gradients of the lines can be calculated and a virtual landscape (DTM) created. Harris (Harris 2000) uses a terrain model to recreate the ancient landscape around an Adena Indian burial mound in Moundsville, West Virginia. | 
