CHAPTER 1: INTRODUCTION TO THE VISUAL RESOURCE ASSESSMENT MODEL AND THE CASE STUDY OF THE COLUMBIA RIVER GORGE

The Visual Resource Assessment Model is a computer based model designed to analyze the visual resource of a regional landscape for the relative ability of its parts to attract attention from people within the landscape. The model does not attempt to determine the relative quality of the landscape, but rather its visual prominence.

Existing models for visual resource analysis have concentrated on tne project, neigoborhood, or town scale. Tne visual concerns of these smaller landscapes were the first to be addressed by research efforts in tne field of landscape architecture. The methods used to address the problems of small scale landscapes included social science surveys, photographic or simulation rating, professional opinion, and data overlay techniques. These methods become cumbersome, expensive, and time consuming when applied to a large regional landscape. An area in excess of 100 square miles can contain a diverse collection of landscapes, and present a staggering quantity of pertinent information for a visual resource analysis.

The large volume of information is best handled by a computer. It performs the mathematical manipulations of the numeric data needed in the most efficient manner. Data can also be easily shared between projects to analyze additional types of resources. Basically, the computer can expand the possibilities of overlay tecnniques (1, 2). Overlay methods simply add multiple layers of data to produce an end result. It introduces the added potential of trend surface analysis, time frame modeling, and statistical analysis of spectral data (3, 4). As studies of visual perception, visual resource management, and social functions of the visual landscape expand our understanding, the developments in computer software will allow analytical techniques to keep pace.

The Visual Resource Assessment Model focuses on the biophysical characteristics of the environment, the source of the stimuli. Visual quality is the result of the interaction between the physical environment and the viewer. The stimuli from the environment are the common denominators in the interaction. Viewers vary greatly in their responses to the visual environment, but they share common physiological responses to stimuli (1).

The higher brain functions ascribe meanings and interpretations to the stimuli. The more complex functions of the cerebral cortex produce the responses studied in surveys and photographic rating procedures.

The elements of the physical environment used in the model are modified by the characteristics of the population selected for study. In the case study of the Columbia River Gorge, a location for the people whose views will be considered was chosen. Viewer-points along I-84 were selected for the calculation of the viewsheds. I-84 is the most common place from which both residents and visitors view the Gorge. This is a limited representation of the places commonly used in the Gorge. The towns, the Oregon Scenic Highway, the Washington Evergreen Highway, and the hiking trails in both of the states should be considered in a detailed study of the Gorge.

The distance element also depends on the location of the people whose views will be used in the model. The distance element is the calculation of zones of distance from the viewers' locations alony the interstate highway to the areas of the landscape.

The elements used in the Visual Resource Assessment Model are viewshed, slope, aspect, distance from the viewer, soils, and reflected light contrast (pixstat). Viewshed is a compilation of the calculations of the viewsheds from nine points along I-84, figured both with and without land cover modifying the topographic data. This yields a measure of the frequency that a portion of tne landscape can be seen, and thus the time exposed to the view of that object. It also indicates where a section of the landscape could be seen if the land cover were changed or removed.