Information intensity deals with the level of detail (LOD) presented in the VE. One issue relevant to LOD is how much detail should be shown at a particular scale. If the purpose is to simulate reality, then the inclination is to show considerable detail, but how much detail is appropriate? For instance, in section 25.4.1, we will see that developers strive for realistic images in virtual cities; but is such realism always necessary? Martin Reddy (2001) developed an approach for specifying the amount of detail that should be shown, presuming that greater detail should appear where humans' vision is most sensitive to detail (in the fovea). His approach, however, is largely perceptual as opposed to cognitive, meaning that it does not consider the information content of the image.
A second issue relevant to LOD is how it should change as scale changes. In Chapter 6, we presented a number of rules that are appropriate for generalizing abstract symbolization for two-dimensional maps, but these rules do not necessarily extend to realistic looking VEs. Those working with the notion of a Digital Earth (see section 25.4.3) have developed approaches for changing detail with scale, but these approaches deal largely with technical issues (e.g., Reddy et al. 1999), no with what users will necessarily need or want. Similarly those working with forested landscapes have developed approaches for changing detail with scale (e.g., Kumsap et al. 2005), but, again, these do not consider the detail that users may need or want.
Those in the field of landscape and urban planning have begun to conduct experimental studies on the LOD appropriate for various applications (e.g., Bishop and Rohrmann 2003, Williams et al. 2007). A key point is that the LOD will depend on the purpose of the visualization. For instance, the conservationist who is inter ested in biodiversity may require a different LOD than someone who is evaluating a landscape for scenic beauty (Williams et al.2907,215)