C O N T E X T 1 1 5 : J U LY 2 0 1 0 11 listed buildings and ancient monuments. However, it is often difficult to assess non-statutory designations, or to determine which professional discipline is best placed to assess them. In certain situations cultural heritage value can counter landscape or townscape value, with the assessment of the landscape setting of historical sites differing as a result of the specific study objectives of the heritage consultant and the landscape professional. Such difficulty often arises in relation to the assessment of derelict industrial sites, where the degraded amenity and character of the townscape can exhibit important examples of industrial heritage. At present the best approach for considering townscape and heritage matters is carefully to review the applicable planning policy and to ensure a close working liaison between landscape and cultural heritage experts during the assessment process. Landscape professionals must remember that an attempt to mitigate adverse townscape impacts of a development could itself have the potential to affect cultural heritage assets adversely. When measuring the success of landscape and visual impact assessment and the subjectivity linked to the process, it is interesting to review the comments made by those with decision-making responsibilities. Many local planning authority officers and Planning Inspectorate representatives acknowledge that the assessment process must be subjective, but informed by thorough baseline capturing, field studies and desktop analysis. Many new techniques have been established to aid the accuracy of assessment. But it is a matter of judgement as to how much of a proposed development is likely to be visible, and to what extent that is acceptable. A major criticism of decision makers is the lack of consistency in approach, the failure to consider the interplay of heritage and landscape effects, and the inability to monitor either the effects of a development or the success of mitigation measures. Of the techniques that have assisted in delivering a more transparent assessment approach, the most common are related to visualising proposals and appraising views to and from the site. Most assessments now include information about the existing and proposed visibility of a site through the computer modelling of a zone of visual influence (ZVI). Derived from a visual envelope map (VEM), which has historically used fieldwork data and Ordnance Survey mapping to predict visibility, the ZVI uses digital mapping to interpolate the visibility of the site and any development proposed. Given that the ZVI is only as accurate as the information used to generate it, it is essential that professionals refine the actual extent of the ZVI by using viewpoint analysis and site photography to plot intervening elements such as terrain, vegetation belts and built form. Used alone, the ZVI still presents only a limited understanding of the visual properties of a landscape – hence the increasing use of verified computerised visualisation to aid the assessment process. Two-dimensional photomontages, wireframe models, rendered views and three-dimensional fly-throughs are all used to varying degrees, depending on the planning status, size or public interest of a development proposal. Such work must always consider the worst-case winter scenario, and be defensible in terms of accuracy and legitimacy. As a tool, visualisation is only descriptive in nature. The hard task of evaluation still needs to be undertaken. Most important, the technology permits development schemes to be adapted easily, and modified to take account of spectrum of opinion and professional judgement. Landscape and visual impact assessment include a combination of objective and subjective judgements, supported by a range of technical work.To ensure that conclusions reached by landscape professionals stand up to public opinion and decision-maker scrutiny, it is crucial to differentiate between judgements that involve a degree of subjectivity (as in the assessment of landscape value) from those that are more objective and quantifiable (as in the determination of magnitude of change experienced). Jonathan Berry is director of Tyler Grange. Left: A verified photomontage illustrating the impact of proposed development parameters and indicative massing blocks on the current visual context of Birkenhead Docks Right: A fully rendered photomontage of a proposed wind farm in Huntingdonshire, used to assess the visual impact on the adjacent parish of Offord D’Arcy. A topographical and digital ZVI analysis has been undertaken using GIS software to determine the likely visibility of a proposed development site in Longhope, Gloucestershire.
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