Visual Impact Assessment
A proposed development can be clearly visible without creating the same degree of visual change from every location. Magnitude of visual change helps describe how substantial that change is within a particular view.
In Brief
Magnitude of visual change describes the nature or extent of the visual change created by a proposed development when viewed from a particular location. Depending on the assessment methodology, considerations may include apparent scale, the proportion of the view affected, distance, screening, contrast and the relationship between the proposal and the existing visual environment. Magnitude is different from visual sensitivity and does not, by itself, determine overall visual impact.
Within a Visual Impact Assessment, magnitude helps describe the change introduced by a proposed development within a particular view. It moves the assessment beyond simply establishing whether the proposal can be seen and considers the nature or extent of the resulting visual change.
The way magnitude is determined depends on the project and assessment methodology. For some projects, apparent scale or the proportion of the view occupied by the proposal may be particularly relevant. Other assessments may also consider matters such as distance, screening, contrast, visual prominence and the relationship between the proposal and existing elements within the view.
Magnitude should therefore not be understood as a universal measurement or a single calculation that applies to every Visual Impact Assessment. It is a structured way of describing the visual change created by the proposal in accordance with the methodology appropriate to the project.
Magnitude and sensitivity describe different parts of the visual relationship between a proposal and the people who may experience it.
Magnitude of visual change concerns the change introduced by the proposal within the relevant view. Visual sensitivity considers the susceptibility or importance of the visual experience being affected, according to the methodology being used.
A substantial visual change does not make a receptor highly sensitive. In the same way, a highly sensitive receptor does not tell us how much of the view will change.
For a closer explanation of the other side of this relationship, see What Is Visual Sensitivity in a Visual Impact Assessment?
There is no single set of magnitude criteria that applies identically to every project. The relevant considerations depend on the type of development, the view being assessed and the applicable methodology.
Depending on those circumstances, magnitude may be influenced by the apparent scale of the proposal, how much of the view is affected, the extent of the development that is visible, distance from the viewer, screening, contrast with existing surroundings and the relationship between new and existing elements within the view.
Viewing direction and the composition of the existing view may also matter. A proposal that occupies a prominent part of one view may appear very differently from another location where it is seen at greater distance, partially screened or among existing built or landscape elements.
This is why magnitude is assessed in relation to particular views rather than inferred solely from the physical dimensions of the development.
Magnitude asks how substantial the proposed visual change is within a particular view. Sensitivity asks how susceptible or important the affected visual experience may be.
The physical size of a development and its apparent size within a view are related, but they are not the same thing.
A large structure viewed from a considerable distance may occupy a relatively small part of the visible scene. The same structure seen from much closer may occupy a substantially greater proportion of the view. Its apparent scale can also be influenced by surrounding buildings, vegetation, landform and other elements that provide visual context.
Some project-specific visual assessment methodologies use measurable aspects of apparent size or field of view when determining visual magnitude. Others may apply a broader combination of quantitative and qualitative considerations.
The important principle is that magnitude concerns how the proposed change presents within the assessed view, rather than physical project size in isolation.
Distance can be an important influence on apparent scale and visual prominence, but distance alone should not be treated as a universal measure of magnitude.
As distance increases, a development will generally occupy less of the viewer's field of view. However, the resulting visual change also depends on the scale and form of the proposal, the amount that remains visible, the surrounding visual context and the assessment methodology being applied.
A distant element may still be visually prominent in an open view, while a closer development may be substantially screened or seen among existing elements of similar form and scale.
Distance is therefore one part of understanding visual change rather than a stand-alone predictor of magnitude.
A proposal is rarely experienced in isolation. Existing vegetation, buildings, landform and other elements may influence how much of the development is visible and how strongly it contrasts with its surroundings.
Screening may reduce the visible extent of a proposal from a particular location, but the presence of screening does not automatically establish a low magnitude of visual change. Its effectiveness depends on matters such as the viewing location, what part of the proposal remains visible and the conditions represented in the assessment.
Existing context can matter in a different way. A new element that is similar in scale, form or visual character to its surroundings may produce a different degree of visual change from an element that introduces a strong contrast into the same view.
These considerations help describe the change within the view. They should not be confused with a separate assessment of geographic visibility or Viewshed Analysis.
Not necessarily. Physical size is relevant, but it does not determine magnitude by itself.
A physically large proposal may appear relatively limited within a broad or distant view. Another proposal with smaller physical dimensions may create a more noticeable change where it is closer, more exposed, more contrasting or occupies a more prominent position within the composition of the view.
This does not mean project size is unimportant. It means that visual magnitude describes the experienced visual change from the relevant assessment location rather than relying on one physical dimension in isolation.
Representative viewpoints are therefore important evidence in understanding how the same development may present differently across the surrounding visual environment. For more on their role, see How Are Viewpoints Selected for a Visual Impact Assessment?
Yes. A relatively limited magnitude of visual change should not automatically be interpreted as meaning that the visual effect is unimportant.
The sensitivity of the relevant visual receptor, viewpoint or visual experience may also need to be considered. A comparatively small change occurring within a sensitive visual setting can therefore require different consideration from the same degree of change in another context.
The reverse is also important. A substantial magnitude of change does not automatically establish the final level of visual impact without considering the wider assessment framework.
Magnitude tells us about the change. It does not, on its own, provide the complete assessment outcome.
No. Magnitude of visual change and visual impact are related concepts, but they should not be used interchangeably.
Magnitude describes an aspect of the change created by the proposal. Visual impact or visual effect is the broader assessment outcome reached through the methodology being applied, which may also consider visual sensitivity and other relevant factors.
This distinction follows the same principle discussed in Visibility vs Visual Impact: knowing that a proposal is visible does not tell us the final visual impact, and knowing the magnitude of change does not provide that conclusion on its own.
Keeping these concepts separate makes it clearer how an assessment moves from observations about a view to a reasoned evaluation of visual effects.
Visual assessment methodologies may consider both the magnitude of visual change and the sensitivity of the affected visual experience when evaluating visual effects.
This creates two distinct questions. First, how substantial is the visual change created by the proposal from the relevant location? Second, how susceptible or important is the visual experience affected by that change?
Some methodologies use defined matrices or rating systems to bring these considerations together. Others may structure the evaluation differently. A matrix from one project type or guideline should therefore not be assumed to apply universally to another assessment.
What matters is that the assessment explains the basis for both considerations and applies the methodology appropriate to the project consistently.
A proposed development does not necessarily have one magnitude of visual change that applies equally from every surrounding location.
Its apparent scale, visible extent, screening, relationship with existing elements and position within the view can change as the viewing location changes. This is one reason representative viewpoints and visual receptors are important within the wider assessment process.
The appropriate way to determine magnitude also depends on the project type, jurisdiction, planning pathway and applicable assessment guidance. A methodology designed for one form of infrastructure should not automatically be treated as the methodology for every Visual Impact Assessment.
A well-structured assessment therefore makes the reasoning visible: what changes within the view, what influences the extent of that change and how the resulting magnitude has been determined for the particular project.
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Magnitude describes the visual change created by a proposal. Understanding its potential visual effects also requires consideration of the sensitivity of the visual experience being affected.
Understand visual sensitivity →Visual Impact Assessment
The appropriate approach to visual magnitude depends on the proposal, viewing conditions, project type and assessment methodology.
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