Take advantage of the search to browse through the World Heritage Centre information.

Note 5

Visual Impact Assessment

A Visual Impact Assessment (VIA) is a specific study that focuses on assessing the visual and aesthetic impacts of a proposed project. This type of assessment is not a stand-alone study but should be part of the study that assesses impacts on the OUV of a World Heritage property (Environmental and Social Impact Assessment, or Heritage Impact Assessment study) – in the most likely case when it is relevant for its values. VIAs are largely used for assessing the impacts of proposed infrastructure projects in relation to cultural World Heritage properties inscribed for their architectural and landscape values. It is to be noted that visual qualities are primarily related to the integrity of a World Heritage property. World Heritage properties that are inscribed on the World Heritage List under the category of cultural landscapes might be especially vulnerable to wind energy developments.

➔ See World Heritage essentials

What should be considered in relation to the World Heritage property/properties?

The visual and aesthetic impacts of wind energy facilities on the landscape are one of the main challenges faced by the wind energy development. The perception of these facilities in a landscape depends on several factors: typology of the site, morphology of the landscape, social factors, the extension of infrastructural development in the area and the level of acceptance by local communities.

Wind energy projects not only need to consider the possible compatibility or incompatibility of wind turbines and ancillary facilities with the attributes that convey the OUV of a World Heritage property, but also need the willingness and support of the people and local communities to live with and adapt to the proposed changes of their environment. Visual aspects, in this respect, play an important role in the acceptance of these projects.

The assessment of the visual impacts of a wind energy project relates directly to the visual qualities of the OUV of properties within their aspect of integrity. From the point of view of World Heritage protection and management, the project should not compromise or marginalize the visual characteristics and attributes of a World Heritage property.

For a VIA in the World Heritage context, consideration should be given to:

  1. the overall sensitivity of a World Heritage property and its setting to changes in general;
  2. the sensitivity of the property to wind energy facilities that includes measuring qualitative and quantitative visual changes, considering particularly the installation of tall facilities like wind turbines or industrial set ups like sub-stations and power grids (for potential dimensions of the parts of a wind farm and ancillary facilities ➔ see Wind energy essentials);
  3. the extent to which a property and its setting can adapt and support change while ensuring the protection of its OUV.

Information related to visual sensitivity of a World Heritage property and its attributes can be collected through the process of vulnerability studies/sensitivity mapping (➔ see Note 2). This process looks at the connection between the property’s OUV and its key panoramas and vistas, as well as intangible connections and ways in which people and communities perceive the property and its surrounding.

A visual impact assessment needs to include a detailed map showing the location of all attributes conveying OUV, all relevant vistas and panoramas, the physical location of the proposed development and any ancillary or annexed facility as well as other existing developments that might need to be considered to assess possible impacts and cumulative impacts. Nevertheless, depending on the characteristics of the property and its OUV, some attributes may be difficult to trace and map, and should therefore be considered beyond their physical location on a map.

➔ See Note 6

The information related to the World Heritage property and the planned wind energy development need to be combined for assessing the potential impacts:

Design and siting of the wind energy development project

Factors potentially creating the impact

Elements that need consideration during the assessment and evaluation of impacts

visibility of wind turbines

  • number of wind turbines
  • design and colour of the turbines
  • rotor diameter
  • hub height and total height of wind turbines
  • lighting of wind turbines at night
  • extent of visibility
  • the surrounding landscape of the installation (natural or man-influenced surroundings with their visual sensitivity)
  • the significance of view sheds

position of wind turbines and their ancillary facilities

  • distribution of wind turbines within the landscape and their position in relation to the World Heritage property and its buffer zone/setting
  • topographical characteristics of the property and its setting
  • distance from important identified view sheds, vistas and panoramas of the property
  • the significance of view sheds, panoramas, or vistas
  • visual relationships between visually important attributes of the property
  • dominance within the topography
  • relationship/ interference with the significant topographic features
  • scale contrast between the wind energy infrastructure and significant features and elements in the landscape
  • conditions of geography, weather, etc.
  • presence of neighbouring artificial structures
  • presence of other artificial structures and existing wind turbines (accumulated impacts)

extent of the development

  • the area covered by the wind energy infrastructure

Visualization of impacts

The digital visualization of wind energy projects to support assessing their impact is at the core of VIAs. The production of a digital visualization requires adequate data, technical material and software. Good simulations or models are:

  • spatially accurate and realistic, simulating the expected appearance of the proposed project and the actual appearance of the property and its setting;
  • representing different views, including different viewpoints, day time/night time differences, weather conditions, lighting conditions, seasons and others;
  • visually clear and accurate including all necessary details of the proposed project and the property;
  • defendable and able to withstand scientific scrutiny.

Accurate and realistic simulations are key during the consultation process in general but are especially important during the engagement with rights-holders and other stakeholders as they allow for people and communities to better understand and contextualize the project in relation to their environment and the World Heritage property.

Tools for visualizing and assessing the impact of proposed and planned wind energy infrastructures in relation to a World Heritage property and its setting could include:

  • digital terrain models (DGM) and digital surface models (DOM) which allow showing precise distances and heights between the property, the viewpoints and the potential placement of the wind turbines, including the topography in-between;
  • Photo simulation and photomontage: photographic-based assessments, like photomontage and modelling, should provide clear technical information concerning the position of the camera and the focal length used for the images used in the montage. This information is vital to prove the reliability of the recommendations derived from the visual impact study;
  • Viewpoint photography;
  • 3D modelling and digital simulations;
  • Colour and light-based methods;
  • Zone of visual influence maps;
  • Line of sight technique which is a digital and GIS-based assessment that applies an accurate representation of the shape of wind energy facilities to better understand the visual perception of these facilities by the human eye. It considers the distortion of the perceived shape and size of facilities caused by the location of the observer and calculates the possible obscuring of facilities caused by terrain morphology. This also allows including information of other existing facilities to represent the landscape more accurately;
  • Landscape sensitivity assessments;
  • Landscape quality assessments;
  • Viewshed analysis in a GIS (or visual envelop) map: a digital evaluation model based on GIS data which is used to determine which parts of a landscape are visible or not visible from a particular vantage point.

Visualization tools

Data requirement


Digital terrain model and digital surface model

Both for DGM and DOM:

  • identification of visually sensitive areas;
  • views to buildings of cultural or historical significance;
  • vantage points and locations frequented by a large number of visitors (walking trails, etc.);
  • views in the direction towards the property (showing silhouettes from outside);

Viewpoints need to be chosen in agreement with all bodies involved.

Advantage: allows immediate depiction and consideration of forests, buildings and obstructing views, etc.

Visualization tools

Data requirement

Technical requirements


photo simulation and photo montage

  • digital terrain and surface models
  • selected viewpoints (vantage points/ observer points)
  • exact location of the wind turbines
  • exact type of the wind turbines
  • adequate software tool for executing the simulation
  • technically adequate photographic material for the simulation

viewpoints from inside the property with views away from it to the outside also need to be considered

for the photographic material:

  • precise geographic coordinates (including altitude) of the camera’s position and viewpoint
  • date and time of the photograph
  • type of camera
  • lighting conditions (front lit, backlit, side lit)
  • type and model of camera and lenses
  • focal distance/ length (35 mm format in digital SRL cameras)
  • width of lens angle (to provide realistic proportions between the landscape and the planned wind energy facilities)
  • record of different weather conditions (including optimal visibility conditions)
  • distance from the proposed development (i.e., wind turbine or other ancillary facilities)
  • dynamic effect of the rotating blades

coloured markings of towers and rotor blades and flashing lights on the nacelles and towers

the description of each photo simulation is very important including information on the viewpoint (taken where and what do we see?), its orientation (with directions and degrees), focal length, etc. and the number of viewpoints

Assessing visual impacts

Potential visual impacts should be evaluated by considering the visual sensitivity of the property combined with the potential magnitude and significance of the impact on the property’s OUV.

The assessment should be based on two key sets of information concerning:

1. Characteristics of the World Heritage property related to identified key visual aspects, scenic views and panoramas, including information on:

  • the topography of the property and the connections within the property, and between the property and its setting;
  • attributes conveying the OUV of the property and values that are not part of the OUV but have a role to support it;
  • key observation points (KOPs) including sensitive areas, panoramas and viewsheds that can support the protection of the OUV.

2. visual characteristics of the proposed wind energy installation, including information on the wind turbines and, if applicable, the ancillary facilities:

  • scale of the wind energy project;
  • location of the wind energy facilities;
  • form of the wind turbines and other facilities;
  • height (hub and with blades) of the wind turbines and other facilities;
  • rotor diameter of the wind turbines;
  • colour, including possible colour contrast of the wind turbines with the surrounding land- or seascape;
  • texture/material of the wind turbines and other facilities;
  • glare of the wind turbines;
  • lighting of the wind turbines;
  • motion of wind turbines;
  • number and distribution of the wind turbines within an area;
  • visual lines and axes of the facilities (paths followed by the eye when perceiving obstructions and abruptions in a landscape).

There are multiple methodologies for the identification of possible visual impacts and many more for the evaluation of these impacts. There is no standard nor a universally or unilaterally agreed methodology to assess the visual impacts of wind energy facilities on a World Heritage property. Therefore, the decision in favour of a specific VIA methodology should be justified by technical considerations about the OUV of the World Heritage property and the proposed wind energy project. Nevertheless, as already mentioned, visual impacts of wind energy projects should never be assessed in isolation but be considered within the scope of a fully fledged World Heritage focused impact assessment and together with other impacts, including environmental, cultural heritage, social and economic impacts.

The methodology applied in the assessment should be described clearly and with specific reference to the evaluation criteria considered during the process. There are various possible typologies of assessments with consolidated scientific and technical requirements, and should all consider with quantitative and qualitative methodologies:

  • the extent of the visibility of a wind energy facility (like maximum vertical angle of visibility, horizontal angle of visibility);
  • the distance of the project and its element that are visible (and wind turbines, other features of the project) from identified key observation points and viewpoints;
  • the number of visible wind turbines and other features of the project (at a given vertical angle and above);
  • the significance of the viewshed;
  • the character of the landscape or seascape, and the surroundings of the installation (natural or man-influenced surroundings with their visual sensitivity relevant for the OUV of the property).

The degree of impacts will need to consider the level of visual intrusion and obstruction in relation to identified sensitive areas or key panoramas and vistas.

Assessing the level of impacts

Degree of impact



A wind energy project is intrusive, dominant and/or extensive with direct impact on the attributes of the OUV and the wider setting of the property. The project would considerably transform the characteristic of the property. (The proposed wind energy project would completely change the character of the setting of the property resulting in negative impacts that cannot be mitigated as they will have major negative effects on the OUV of the property).


A wind energy project is noticeable and with potential impact on the property or part of its OUV.

Wind turbines and ancillary facilities are an uncharacteristic element in the property and its landscape. (This could result in the wind energy installation being out of scale with regards to attributes of a property’s OUV or they might be located somewhat visibly inside a key view or panorama).


The visual changes introduced by the wind energy project are limited and do not completely alter the characteristics of the property and its setting. (Mitigation measures could be considered to avoid any negative visual impact).


The proposed wind energy project consists of a visual change, which is not perceptible. (The proposed project has no visible negative impact on the property and its OUV. This could be the case of projects complementing or maintaining the scale and quality of the surrounding landscape).

Table: Magnitude of impact, adapted from Apostol et al. (2016).

Examples of potential visual impacts of wind turbines on the OUV of World Heritage properties are listed as below

Potential type of impact



Technology overload effect

The technology overload effect arises when the number of technological items in an area increases to a point that their visual presence overweighs the character of the embedding or juxtaposed cultural landscape with its natural and cultural historical structures and elements.

  • Natural landscapes and elements of natural beauty and aesthetic importance in a landscape may be considerably altered, cultural and historical buildings may lose their importance on the horizon, and views may be disrupted.

Visual dominance

The visual dominance is a consequence of the size and the high visibility of wind turbines; the observer recognizes primarily the huge wind turbines instead of the cultural or natural heritage elements or the natural phenomena in a landscape.

  • The wind turbines alter the existing harmonious relationships between the different characteristics and elements of natural beauty and aesthetic importance in a landscape.
  • The movement of the rotors create a ‘disquieting’ effect in the landscape and disturb the natural tranquillity.

Loss of scale

The effect of a loss of scale means that, beside the new technical installations of wind turbines, well-known big natural elements like trees or cultural elements, such as towers or castles, visually shrink and become dwarfish. The new scale is out of proportion.

  • The scale of visual influence and of impairment is such that the turbines and related facilities let the surrounding buildings, natural features and elements of natural beauty and aesthetic importance in a landscape shrink and affect their values.

‘Barrier effect’

This is generally caused by the alignment of wind turbines creating a visually present barrier between different landscape elements.

  • The wind turbines may cut through a landscape and interrupt key views and the interrelationships between different landscape features or interrupt key views that are part of the OUV, or furthermore, separate the World Heritage property from its embedding landscape.
  • The continuity of a landscape with view axes from short and long distances may get lost.
  • See case studies in World Heritage and Wind Energy Planning (2021)
  • In 2013, the Landscape Institute for Environmental Management and Assessment (IEMA) published a Guidelines for Landscape and Visual Impact Assessment (GLVIA3).This is a key resource for those involved in assessing visual impacts or reviewing an impact assessment report including specific references to the assessment of visual and landscape impacts. Although the guidance is not a World Heritage specific document and does not focus on the OUV of World Heritage properties, it nevertheless could serve as key guidance for the assessment of a property’s visual sensibility and for the identification and evaluation of possible visual impacts.
  • A useful document prepared by the NGO Kompetenzzentrum Naturschutz und Energiewende facilitate wind energy project planning in Germany (available in German).
  • A study on visual integrity has been prepared for the Dutch Water Defence Lines World Heritage property (the Netherlands) on assessing visual impacts.