Zone of theoretical visibility maps

Zone of theoretical visibility maps

Zone of theoretical visibility maps

Most landscape or townscape assessments will include Zone of Theoretical Visibility (ZTV) maps, which show the area from which an object could theoretically be seen. ZTVs are based on digital terrain models (DTMs).

There are two principal types of ZTV:

  • Bareground: where the underlying model just represents the topography, without screening vegetation or structures. These ZTVs depict the worst-case scenario.
  • Screened: where the model includes topography as well as screening features.

Clicking through the images below allows comparison of a bareground and screened ZTV for the same study area. Both are based on the same digital terrain model. The screened ZTV also takes into account the principal blocks of woodland as screening elements. The screened ZTV indicates a much reduced theoretical visibility compared to the bareground ZTV. Fieldwork confirmed the screened ZTV to be the more realistic depiction of theoretical views experienced near the site. However, features not included in the screening layer such as hedgerows, field trees and garden vegetation were confirmed to further reduce the extent of views compared to the screened ZTV model.

How ZTVs are calculated

A digital terrain model can be produced from various mapping sources. In the UK we commonly use Ordnance Survey terrain data, either the freely-available Terrain 50, or Terrain 5. Terrain 50 has an elevation value for each 50m by 50m area, which means the data is useful for very large areas or for initial, broad-brush studies. Terrain 5 has an elevation value for each 5m by 5m area and common data for producing ZTVs of development proposals where the LVIA study area may be between 2 and 5km from the site.

ZTVs are normally produced using scripts in Geographical Information System (GIS) software. The scripts can take into account earth curvature and atmospheric refraction (bending) of light, which influence visibility especially in more distant views. For example, viewpoints for wind farms may often be well 10 to 25km from the development.

Examples of ZTVs

Wind farm ZTV

The plan below is a bareground ZTV for a single wind turbine. The ZTV is based on OS Terrain 50 and has been calculated to different heights to gain an understanding of where different parts of the turbine would be visible (e.g., the hub or the blade tips).

Wind turbine ZTV plan

Wind turbine bareground ZTV plan (OS Terrain 50 digital terrain model)

Fine-grained ZTV for tall building project

The image below shows a ZTV of a proposed tall building development. The ZTV is based on a digital surface model (DSM) comprised of Lidar survey data from the Environment Agency. The DSM shows 1m resolution data (an elevation reading for every 1m by 1m square) and includes buildings, vegetation and other surface features. In urban areas, this more detailed approach to ZTV modelling can be useful in identifying key view corridors along streets so helping to identify very specific potential views to a proposed development. In rural areas, the Lidar survey picks up hedgerows so ZTVs based on this data can give a more refined indication of theoretical visibility. Note that the ZTV output is theoretical and still requires interpretation. For example, theoretical visibility on the plan below is indicated from the roofs of buildings, which would not normally offer accessible public viewpoints.

Lidar-based ZTV

ZTV based on 1m Lidar survey data (Environment Agency)

Visibility index

We can also use ZTV techniques to look at the relative visual exposure of a landscape. The visibility index (VI) is theoretical output which gives an estimate the size of the ZTV for each grid cell in a digital terrain model. This can be very useful where there is a large site, only part of which is required for the proposed development. The VI calculation can help identify areas of lower or higher sensitivity. An example VI map is provided below. The red areas are relatively more visible from other parts of the DTM than the blue areas.

Visibility index

Visibility index plan, showing the relative visual exposure of the area covered by the digital terrain model

Interpretation of ZTVs

A ZTV shows the theoretical areas from where a development would be visible or not. The ZTV does not indicate the nature or significance of effects which would be likely to arise.

ZTVs can be very useful in early project stages to help identify the main areas of potential views. This can assist in locating assessment viewpoints and highlighting key receptors.

ZTV analysis can also be very useful in comparing development options, for example layouts which use different parts of a residential site, or different wind turbine heights.

It should be borne in mind that a ZTV will only be as accurate as the data on which it is based. It is normal for the landscape architect to verify the representativeness of the ZTV when doing LVIA site work.


ZTVs are potentially a powerful tool for landscape and townscape assessment work. There are various methods and data which can be used to produce ZTVs. Their application and interpretation needs careful consideration. In particular, it should be remembered that they only illustrate theoretical visibility.

Take a look at some of our projects, most of which will have involved some sort of ZTV modelling.

Townscape assessment

Townscape assessment

Townscape assessment

This note gives a brief, non-technical overview of townscape character assessment and the role it plays in urban planning.

Townscape character assessment (TCA) plays a key role in integrating urban development into its wider townscape context. It’s often important to gain an understanding of existing townscape character in the early stages of an urban development project.

Landscape Visual Limited has undertaken TCAs and townscape and visual impact assessments (TVIAs) for a wide variety of urban projects, including large-scale regeneration schemes and taller buildings. This work is informed by a number of documents, including the Landscape Institute’s Technical Bulletin 05/2017 and the Guidelines for Landscape and Visual Impact Assessment (GLVIA3).


Key components of townscape character

Townscape character evolves through the interaction of a range of physical, social and cultural components. How these components are understood and experienced by people is an integral part of townscape character.

TCA includes consideration of:

  • The historical development of the urban environment.
  • Any cultural associations and heritage assets.
  • The existing urban structure and urban grain
  • The massing and scale of existing built form.
  • Legibility, landmarks, vistas and skyline.
  • Green infrastructure, streetscapes and the public realm.
  • Utilities, movement and connectivity.
  • Perceptual qualities, such as levels of relative tranquillity.

The TCA process analyses the spatial arrangements, relationships and narratives that are created when the above components come together. This in turn allows a tangible sense of place to be distinguished and clearly articulated.

As part of our townscape and visual impact assessment work, we will often map the local townscape character. This gives a baseline against which changes brought about by a proposed development can be assessed. The example below was produced for an area undergoing profound transformation near Hayes and Harlington Station in the London Borough of Hillingdon.

Townscape character assessment plan

Townscape character assessment plan: near Hayes and Harlington Station, London Borough of Hillingdon


The role of visualisations in assessing townscape and visual effects

Photomontages, verified views or accurate visual representations (AVRs), are a central part of TVIA work, particularly where tall buildings are proposed (read more here). AVRs can include wireframes or rendered photomontages. AVRs from key viewpoints can be a very useful tool when considering the scale, massing and height of new development in relation to:

  • The scale, mass, height and architectural design of adjoining buildings.
  • The general pattern of building heights in relation to landform, vegetation and the skyline.
  • Existing key views, vistas and landmarks.

Visualisations were an important part of our TVIA work for a taller building development in Shoreham Harbour. The photomontages we prepared illustrated how the proposal related successfully to its townscape context, including neighbouring residential streets.

Townscape character assessment

Townscape character assessment: Boundary Road, Portslade-by-Sea

Click through the images below for examples of some townscape assessment projects.

LVIA Photography

LVIA Photography

LVIA Photography

Photographs are used extensively in landscape / townscape and visual impact assessment (LVIA / TVIA).

In baseline assessment (i.e. describing the existing landscape) photographs are normally used to illustrate the existing landscape character. Typically, an LVIA will include photographs of the site and the surrounding landscape character areas.

Assessment work normally uses representative viewpoints and photographs are taken from these viewpoints. Sometimes these photographs are taken in winter and summer (to show the effect of seasonal vegetation) or at night as well as during the day. Viewpoint photographs can be used as back-plate images for photomontages of a proposed development (more detail in our post on Photomontages for LVIA and TVIA).



LVIA photography is undertaken in accordance with:

  • Guidelines for Landscape and Visual Impact Assessment (‘GLVIA3’) (Landscape Institute and Institute of Environmental Management and Assessment, 2013)
  • Landscape Institute Advice Note 1/11 Advice on photography and photomontage.

The latter is currently in the process of being revised (and should be published in 2019) and so now seems a good opportunity to describe in a bit more detail what LVIA photography involves.


Equipment used in LVIA photography


We use a Canon DSLR with a full frame CMOS sensor for all viewpoint photography. ‘Full frame’ means that the sensor is the same size as a single frame of 35mm film. These cameras are professional equipment and can take high quality photographs, with image size greater than 20 effective megapixels.


Lens selection depends on the viewpoint’s context, the type of development and the end use of the photograph. For most LVIA work, a 50mm fixed focal length prime lens is used. While this is generally the agreed standard for LVIA work, there are situations when wide or telephoto prime lenses are used. Some situations (e.g. a near viewpoint of a proposed tall building) require a wide angle tilt-shift lens. This type of lens allows the central axis to be shifted by a known amount to accommodate a tall element while retaining a level camera. These tilt-shift lenses also minimise distortion compared to standard wide-angle lenses (e.g., eliminating converging parallels on buildings).


A strong tripod is always used for LVIA work. The tripod head includes a three-way levelling plate and an indexed rotator. The rotator can be set to a specific interval between frames (e.g. 20 degrees might be used for a 50mm lens with a 40 degrees horizontal field of view) and is essential for creating accurate panoramic photos if a wide field of view needs to be photographed. The tripod head also has a plate for centering the nodal point of the lens with the axis of rotation. This eliminates parallax error when taking panoramic photos. For viewpoints on soft surfaces, spiked feet are used to ensure that the tripod does not move when photographs are being taken. This can be essential when taking photographs on a windy day on a Scottish hillside or Cornish beach.

LVIA photography

A sturdy tripod is essential for LVIA photography. A bike can be very useful too. 

Other equipment

  • A hand-held GPS device to record the viewpoint location.
  • Mapping and a plan for the day’s photography (for example, we always make sure that photographs are taken at the correct time relative to the position of the sun). Mapping typically includes Zone of Theoretical Visibility plans and context plans, including Ordnance Survey mapping and aerial photography.
  • Spirit levels to check the levelling of the camera.
  • Survey marking equipment if we are putting down marks for a survey team (for Accurate Visual Representations / Verified Views – more information in this article here). This can also be useful if we need to return to take photographs from exactly the same location at a different time of day or in another season.
  • A notebook for recording information relating to the photography.

Tripod head for LVIA photography

A tripod head suitable for LVIA photography: a levelling base, a rotator (for panoramic shots) and a plate for adjusting the position of the nodal point of the lens


Examples of LVIA photographs

While it can be the case that guidance is very prescriptive (e.g. photography and photomontage guidance for wind farms such as Scottish Natural Heritage’s Visual Representation of Wind Farms (2017)) there is no substitute for experience in the field. We have undertaken photography in a wide variety of situations from busy urban shopping streets, protected vistas in London, listed buildings and historic landscapes, green belt farmland, and the summits of Scottish mountains. Should you have a project you wish to discuss or would like to find out more in general about landscape / townscape and visual impact assessment work, do get in touch.

Click through the images below for some examples of LVIA photography we have undertaken recently.

Photomontages for LVIA and TVIA

Photomontages for LVIA and TVIA

Photomontages for LVIA and TVIA

Many Landscape or Townscape and Visual Impact Assessments (LVIAs / TVIAs) require photomontages as supporting material. This post introduces what is involved.


Overview of photomontages for LVIA

Photomontages illustrate the location, size, degree of visibility or appearance of a proposed development. There are various techniques which can be used to produce them.

Firstly, high-quality photographs are required. These need to be taken carefully using professional equipment. There is more information on LVIA photography in this blog post.

For LVIA work, photomontages are often verified by a viewpoint survey, which records the location of the camera and fixed reference points in the view to a high degree of accuracy. The survey data is used in CAD or 3d modelling software, which also contains a 3d model of the proposal.

In the 3d software (CAD, 3d Studio Max, Rhinoceros or similar), a virtual camera is created at the surveyed camera location. This virtual camera is calibrated to have the same parameters as the DSLR used to take the viewpoint photograph. By aligning the surveyed reference points with those on the viewpoint photo, a highly accurate photomontage can be produced. These are often referred to as accurate visual representations (AVRs) or ‘verified views’.

Notably, the resulting photomontage would be reproducible by another specialist using the same data and method. This means that the images can be considered reliable. In any project which may be placed under scrutiny due to its impact on landscape and views, this can be very worthwhile. It is of course worth noting however that any image will only be as reliable as the data and method which is used to create it.


Types of Accurate Visual Representation

The most basic AVRs (AVR level 0 or 1) show the location and massing of a proposed development as a simple outline (often referred to as a ‘wireline’). The most elaborate AVRs (AVR level 3) demonstrate how a development would appear in context and under the lighting and weather conditions of the back-plate photograph.

The London View Management Framework (Mayor of London, 2012) uses the following classification for types of AVRs.

AVR type
AVR level 0 Location and size of proposal
AVR level 1 Location, size and degree of visibility of proposal
AVR level 2 As level 1 + description of architectural form
AVR level 3 As level 2 + use of materials


The choice of what level of AVR to produce depends on its end-purpose and practical aspects, including budget. Images showing detailed architecture and landscaping can be very time-consuming to produce.


Examples of Accurate Visual Representations

The image below is an AVR 1 for a commercial development in Newhaven, East Sussex.

An example of an AVR level 1 'wireline' image

An example of an AVR level 1: a commercial development in Newhaven, East Sussex, shown as a yellow wireline


The images below show a viewpoint at Wild Park, in the South Downs National Park, on the edge of Coldean, Brighton and Hove. The first image is an AVR 2, which shows an architectural model ‘block-rendered’ in a neutral colour. The second image is an AVR 3, and shows materials and colour. More sophisticated rendering techniques and lighting and environment settings were used in producing the AVR 3.

An example of an AVR level 2 'block-rendered' image

An example of an AVR level 2 (block-rendered in a neutral colour): Coldean from Wild Park in the South Downs National Park

An example of an AVR level 3 'fully rendered' image

The same viewpoint as above to AVR level 3, showing architectural detail and materials

Guidance for photomontages

There is various guidance which is relevant to the preparation of photomontages:

Sector or local guidance sometimes stipulates the requirements for material submitted with planning applications. Examples include:

  • Visual Representation of Wind Farms (Scottish Natural Heritage, 2017).
  • London View Management Framework supplementary planning guidance (London Plan 2011 Implementation Framework) (Mayor of London, March 2012).

The following image illustrates part of the output required by SNH’s wind farm guidance.


Wireline image of a wind turbine development

Baseline panorama and matched wireline as required by Scottish Natural Heritage’s Visual representation of wind farm guidance (cylindrical projection, image size 820mm by 130mm)












Photomontages often play an important role in landscape and townscape assessment. There is various guidance for producing photomontages for LVIA. However, none of this guidance details the exact methods or techniques to be used in actually producing the images. There are many different approaches and techniques which can be used, the approach normally being tailored to the project type and context. The production of photomontages can require the input of various specialists, including experienced photographers, surveyors and 3d-visualisers. Landscape Visual can produce high-quality photomontages as an integrated part of our LVIA / TVIA work.

If you would like to find out more about how we could help with your project, or if you would just like to find out more about any aspect of landscape planning, please get in touch.

An Overview of Landscape and Visual Impact Assessment

An Overview of Landscape and Visual Impact Assessment

An Overview of Landscape and Visual Impact Assessment

This note gives a brief overview of landscape and visual impact assessment (LVIA). It is intended as a summary, non-technical introduction.

Our LVIA work is undertaken in accordance with the relevant guidance on landscape and visual assessment. The overarching reference is the Guidelines for Landscape and Visual Impact Assessment 3rd Edition (LI and IEMA, 2013). There may be other references which are important depending on the development type and location. An important aspect of LVIA is that there is no ‘standard methodology’; the experienced landscape professional needs to interpret and apply the Guidelines for Landscape and Visual Impact Assessment in devising the approach for a specific project.


What is landscape?

The European Landscape Convention (ELC) defines landscape as ‘…an area, as perceived by people, whose character is the result of the action or interaction of natural and/or human factors’ (Council of Europe, 2000). The ELC supports a holistic approach to landscape planning and covers ‘…natural, rural, urban and peri-urban areas. It includes land, inland water and marine areas. It concerns landscapes that might be considered outstanding as well as everyday or degraded landscapes.


Photo: Planning for landscape change in everyday or degraded landscapes


The scope of LVIA

The scope of LVIA is derived from the Town and Country Planning (Environmental Impact Assessment) Regulations 2017, Schedule 4 of which states that Environmental Impact Assessment (EIA) must include ‘A description of the factors specified in regulation 4(2) likely to be significantly affected by the development: population, human health, biodiversity (for example fauna and flora), land (for example land take), soil (for example organic matter, erosion, compaction, sealing), water (for example hydromorphological changes, quantity and quality), air, climate (for example greenhouse gas emissions, impacts relevant to adaptation), material assets, cultural heritage, including architectural and archaeological aspects, and landscape.’ With respect to landscape and views, an LVIA typically considers the direct and indirect effects of a Proposal, its potential cumulative effects, considers the changes which would arise over time, and whether those changes would be beneficial or adverse.

Landscape and visual effects are considered separately as ‘related but very different considerations’ (LI and IEMA, 2013):

  • Landscape assessment considers the effects of the proposed development on the landscape as a resource.
  • Visual assessment considers the effects of the proposed development on specific views and on the general visual amenity experienced by people.

The LVIA process

The key stages in LVIA are:

  • Describing the existing landscape and visual environment, including information on the value attached to the different resources.
  • Describing the proposed development and its main features or parameters.
  • The systematic identification and description of effects which are likely to occur.
  • The assessment of the significance of effects, focussing on ‘likely significant effects’.
  • Identification of mitigation measures (measures designed to avoid, reduce or offset significant negative effects).
  • Preparation of the LVIA report and other graphic material which would typically include plans, zone of theoretical visibility maps, photographs of the existing landscape, and potentially also photomontages or accurate visual representations of the proposed development.


Photo: Shoreham harbour seascape

LVIA assessment criteria

The following are the main terms used in LVIA:

  • The sensitivity of landscape receptors (aspects of the landscape resource that have the potential to be affected by the proposal) and visual receptors (people whose views may be affected), which depends upon the value attached to the aspect of landscape or view and its susceptibility to harm due to the development proposal.
  • The magnitude of an effect (the change brought about by the development proposal), which depends upon the scale and geographical extent of the change, and its duration and reversibility.
  • The significance of an effect, which depends on the receptor’s sensitivity and the magnitude of the effect.

The component parts of each of these factors are typically combined using matrices, and described using word scales. For example, ‘magnitude’ might be described according to a six-point scale (negligible, very small, small, medium, large, very large); each of these ratings would be defined in the assessment methodology.

The above factors are determined using a combination of quantitative (objective) and qualitative (subjective) methods, and are assessed using professional judgement.


LVIA or landscape appraisal?

LVIA can be carried out as part of the EIA process, or as a standalone landscape appraisal.

Where development is screened as requiring EIA, the LVIA will normally be an individual EIA topic (others including for example ecology, heritage, hydrology and soils). Often, the full LVIA might form a technical appendix to a summary EIA chapter. LVIA work can also inform site selection and consideration of alternatives, and EIA screening and scoping stages (for example, the LVIA consultant might provide preliminary information for an EIA scoping report).

A landscape appraisal is a more flexible and informal process but one which is normally structured to take account of the key LVIA stages listed above. The main difference is that a landscape appraisal does not identify ‘likely significant effects’ as the appraisal is not being undertaken as part of the EIA process.

The EIA Directive (The assessment of the effects of certain public and private projects on the environment (2011/92/EU)) states that ‘Development consent for public and private projects which are likely to have significant effects on the environment should be granted only after an assessment of the likely significant environmental effects of those projects has been carried out.’ The emphasis on likely significant effects is important. It means that LVIA work should be to proportional to the scale of the project being assessed and the nature of its effects. This is true whether LVIA is undertaken as part of the formal EIA process or as an informal standalone landscape appraisal.


Photo: Sub-urban grain and the downland fringe near Brighton



This note has given a brief overview of LVIA, and some background and an explanation of what might be involved. If LVIA work is required, there will usually be a range of practical factors to consider, which could include for example:

  • Consultation with planning officers and statutory bodies;
  • The preparation of photomontages or other visualisations;
  • The co-ordination and programing of LVIA with other parts of the planning submission; and
  • The timing of LVIA photography for winter or summer views.

If you want to find out more, browse through the Guidelines to Landscape and Visual Impact Assessment, or feel free to contact us for some informal advice about your project.

NPPF paragraph 170: ‘valued landscape’

NPPF paragraph 170: ‘valued landscape’

NPPF paragraph 170: ‘valued landscape’

Paragraph 170 of the NPPF states: ‘Planning policies and decisions should contribute to and enhance the natural and local environment by…protecting and enhancing valued landscapes…’

We’ve had several projects recently where determining authorities have asserted that development proposals would be in conflict with paragraph 170 of the NPPF (as updated from paragraph 109) due to the site or context being a ‘valued landscape’. ‘Valued landscape’ is not defined in the NPPF and case law has been instructive in clarifying the situation.

Recent case law in relation to NPPF paragraph 170[1] (CO/4082/2014) and (CO/978/2016) is clear in distinguishing designated landscapes from ‘valued landscapes’. To be considered a ‘valued landscape’, a landscape needs to demonstrate physical attributes which take it out of the ordinary.

Factors which might be considered are set out in the table below, which is based on information derived from Box 5.1 of the Guidelines for Landscape and Visual Impact Assessment. This is also referred to in recent case law relating to ‘valued landscapes’ (CO/978/2016).

Landscape quality (condition)The physical state of the landscape. To what extent is typical character represented in individual areas? How intact is the landscape? What is the condition of individual elements?
Scenic qualityTo what extent does the landscape appeal to the senses (primarily, but not limited to, the visual senses)?
RarityAre there rare elements or features present? Or is the landscape a rare character type?
RepresentativenessDoes the landscape contain a particular character, or elements or features which are particularly important examples?
Conservation interestsAre there ecology, heritage, geological, or archaeological features which are of particular interest (i.e. which add to the value of the landscape)?
Recreation valueIs the landscape valued for recreation where experience of the landscape is important?
Perceptual aspectsIs the landscape valued for its perceptual qualities, notably wilderness or tranquillity?
AssociationsIs the landscape associated with particular people, such as artists or writers, or events in history that contribute to perceptions of the area?
Table above: Factors which might be considered with respect to landscape value (adapted from The Guidelines for Landscape and Visual Impact Assessment, 2013, which is based on Swanwick and LUC, 2002)

Any development site would need to be assessed carefully according to the above factors on its own merits. Recent project experience indicates that, while there can be positive values associated with a site, it is possible that none may be such that the site should be considered a ‘valued landscape’. We have been involved in sites within open countryside in an AONB which are generally of positive character but which do not contain physical attributes which indicate that they should be considered a ‘valued landscape’.

Clearly, discussion of ‘valued landscape’ is a little academic outside of the context of a specific development proposal and its landscape. Determination of landscape value forms an important part of our LVIA methodology. Feasibility studies or landscape appraisals which form part of an evidence base for site promotion might also consider landscape value. If you wish to speak to us about a site where you think these or related issues may be important to the success of your project, please get in touch.

Footnotes: [1] Stroud DC vs Secretary of State for Communities and Local Government (CO/4082/2014); and Forest of Dean DC vs Secretary of State for Communities and Local Government and Gladman Developments (CO/978/2016).

Photo: The High Weald in East Sussex – designated an AONB but not necessarily a ‘valued landscape’

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