A Zone of Visual Influence (ZVI) is used to identify where a development is actually visible from. ZVI’s are used to identify the parts of a landscape that will be affected by a particular development.

The term Zone of Theoretical Visibility (ZTV) is used to describe the area in which a development can, in theory be seen. In reality there may not be visibility because of atmospheric conditions and distance to the development or the screening affects of buildings or vegetation which are not represented by the Digital Terrain Model (DTM). A DTM would consist of bald earth or bare terrain data because this produces the preferred worst case scenario ZTV as surface features change.

The ZVI and ZTV methodologies can be applied to various types of tall developments, from wind turbines to large buildings. In both cases, the curvature of the Earth would always be allowed for. These studies can then be represented on a choice of background maps.