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STIRLING BEFORE PYLONS: Opposing the Beauly to Denny power line in the Stirling area

Briefing no. 6: Visual impact assessments: The limitations of photography and photomontages

June 2006

The Environmental Statement (ES) submitted to support the proposals to build a new 400 kV power line on overhead wires from Beauly to Denny includes a number of assessments of the visual impact of the completed line, as seen with or from key points. Volume 2 of the ES ("Environmental Statement Figures") includes a set of photomontages to illustrate this, in Chapter 24 (to be found on CD number 3) and Chapter 25 (on CD number 4). Volume 5 of the ES ("Technical Annexes - Figures") includes wireline visualisations in Technical Annex 24 (on CDs numbers 7 and 8).

Anyone knowing the locations represented in these figures may feel somewhat frustrated at how little they show, particularly if it is the printed paper versions they are viewing.

Scottish Natural Heritage (SNH) are clearly aware that there is a great deal of concern about the adequacy of visual representations, and are developing Good Practice Guidance for the visual analysis of windfarms, in conjunction with the Scottish Renewables Forum and the Scottish Society of Directors of Planning.

At a recent SNH seminar on this topic, Caroline Stanton, of Horner & Maclennan consultants, set out a number of useful pointers about the process of visual impact assessment. These pointers are as relevant to the assessment of the impact of power lines and pylons (which were also referred to at the seminar) as they are to the assessment of windfarms. The following notes are taken from Ms Stanton's presentation.

1. It is of course desired to make visualisations "true to life" - but the experience of a view can never be truly replicated by a 2-dimensional image.

2. Attempting to reproduce the visual experience of the actual situation is dependent on both:

• The resolution of the image, to ensure sufficient detail is captured; and
• The degree of contrast in the image, to ensure that the detail is visible.

3. A good camera is capable of capturing a level of resolution that is greater than that achievable by the naked eye. However, the natural eye, on a bright day outdoors, can accommodate a contrast ratio of 1,000:1. That is, the eye can take in and see at one and the same time both an object that is in deep shadow, and another that is in light that is 1,000 times brighter. The highest contrast ratio that can be reproduced by even a good quality computer monitor is, however, only 100:1 - and the best printed image manages no more than a contrast ratio of 10:1.

4. As a consequence:

• A photograph can never replicate the experience of a view on site;
• The best camera can only capture a limited range of contrast, limiting the detail that can actually be seen in the image, and
• This range is reduced further when reproduced upon the printed page.

5. Visualisations do have a role, but that is as a tool, an aid, to illustrate the assessments as written down in words. Those assessments should have been carried out on site, independently of the visualisations, and need to be read as the principal evidence of the assessment. The visualisations provide information that:

• Illustrates the background to the written assessment,
• Helps illuminate on what the assessor bases his / her judgement, and
• Aids understanding of the assessors' judgements,

but that information is always and inevitably subject to the inherent limitations of photographs and photomontages.

6. There can be no substitute for professional assessment on site, which is the only way in which the actual visual impacts of a proposed development can be truly recognised.

7. SNH's Good Practice Guidance offers advice on how photographers should select the image size, the viewing distance of the image, the field of view, lens length, etc. Common problems noted in visual impact material submitted in the past include:

• Images too short (with sky and foreground removed)
• Images too narrow (with the context of the view removed)
• Images too small (with too short a viewing distance)
• Too much information in too small an image.

8. Photography and photomontages should represent the best weather conditions, in order to maximise the degree of clarity and contrast in the image. This will still inevitably fail to indicate the actual impacts.

In the second session of the seminar, Ian MacAulay, of Envision consultants, endorsed the points made by Ms Stanton and added a number of further ones:

• On a map showing different circumstances (such as the number of pylons visible from various areas) it is appropriate to use contrasting colours of equal weight to represent the different conditions, not different shades of the same colour. The latter may imply differentials in impact which it is improper to assume to be the reality.
• Viewpoints for photography and photomontage must be chosen very carefully, as those from where there is likely to be the greatest visual effect. A number of viewpoints may be needed, and the list should be seen as provisional, and open to being gradually refined, in consultation with those with a legitimate concern about the proposals.
• Crucial detail can be lost in photographs, not only from the limitations of screen and print contrast ratios, but also through the choice of lens length. A demonstration was given of how three apparently identical images of a landscape, taken with 3 different lengths of camera lens, resulted in detail that could be discerned from one image being invisible in the other two.

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Finally, in the afternoon panel discussion, the point was made that "power lines and pylons are particularly hard to represent in photomontages".

The seminar, "Visual Analysis of Windfarms", was held by Scottish Natural Heritage at Battleby, on 3 November 2005.

Other methodologies: The Virtual Landscape Centre, University of Stirling

There are other ways of making visual representations of the effects of power lines etc on landscapes. The Virtual Landscape Centre at the University of Stirling, for example, uses sophisticated modelling technologies to combine map data, including elevations, with photography, to produce 3-dimensional computer images of landscapes. These can be moved around at will, changing the viewpoint, the elevation of view, the scale, etc, to gain a much more robust and flexible approach to visualisation.

For further details, contact:

Peter Pearson - phone: 01786 833399; e-mail: peter@baker-pearson.net

Nicki Baker - phone 01786 833399; e-mail: nicki@baker-pearson.net

Website: http://www.stirlingbeforepylons.org/

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