Visual Impact Assessment Guidebook

Table of Contents

Appendix 4

Completing visual force and land feature analyses

The purpose of this appendix is to explain how visual force and land feature analyses are carried out (see the Visual Landscape Design Training Manual, 1994).

Visual force analysis

The visual force concept is based on the premise that, as we observe the landscape, our eyes are drawn up hollows and down ridge lines. Learning how to map this concept is critical to developing cutblock designs that better fit the natural landscape. Lines of force are mapped in plan and perspective view using different colours and weights of arrows: red arrows are drawn down ridges and green arrows up hollows.

Mapping procedures

1. Identify and label all major peaks, summits, ridges, and saddles on both the photograph(s) and topographic maps. These landmarks will help make the transition between plan and perspective easier.
2. Starting on the photograph pick out either the convexities or the concavities and complete each set before working on the other. Often it is easiest to start with the convexities. Using a red felt-tip pen identify the major convexities and ridges. Try to ensure that the lines follow the apexes of the ridges as far as they can be traced. Transpose the lines identified on the photo to the contour map as you go.
3. Identify secondary-strength ridges, which will tend to spring from the primary ones. A branching pattern may well emerge. It is usual to find that the number and structure of arrows relates closely to the structure of the landform. There are naturally going to be more force lines in a broken, jagged landform than in a smooth, flowing one. There may be three or four levels in the hierarchy of forces, shown by different thicknesses of arrows.
4. When the mapping of the convexities is completed, repeat the process with a green felt-tip pen on the concavities. Some of the major hollows will coincide with streams or rivers, while others may be dry. Occasionally, stream features are not associated with readily identifiable hollows; in that case, they should be ignored. A connected, dendritic system of green arrows is usual.

Figure A4.1 Visual force analysis in perspective and plan view. Red arrows show major peaks, summits, ridges, and saddles; green arrows show major valleys and gullies (from the Visual Landscape Design Training Manual, 1994).

A landform analysis in perspective view

The same analysis on a plan view of the landscape

Notes:

• In no circumstances should a red arrow cross a green arrow, or vice versa.
• If either the hollows or convexities are generally more dominant, then the primary arrows should be thicker to emphasize this; this may have an impact on the later design.
• It is possible that the contour maps, by reason of their resolution and the spacing of the contour lines, do not show all the visible features of the landform. In this case, additional arrows can be added from analysis of the photograph.
• Conversely, working from a photograph can be misleading when mature forest hides the topography and smooths over subtleties in the landform. It is important to try to look beneath the canopy because if logging takes place, the topography will be revealed.
• On completion, the structure of the topography should have become very clear. The very action of drawing the arrows will help to get the feel of the landform.
• Three-dimensional computer simulations of the views help to show what lies beneath the trees, or can be used to produce different viewpoints with the visual forces in place. This can help to show how the relative strengths of different parts of the landform vary depending on the viewer position.

Using visual force lines

After mapping the visual force lines in perspective and plan view, they are used to guide cutblock design. When cutblocks are being designed, they should respond to visual force analysis mapping in plan view, by pushing up in gullies (green arrows) and dropping down on ridge lines (red arrows). The weight of the arrow will dictate the amount of response. The thicker the arrow, the stronger the response; the thinner the arrow, the weaker the response.

Land feature analysis

This analysis builds on the visual landscape inventory and identifies all the various features in the landscape that make up its character and diversity, its visual absorption capability (VAC), and its existing visual condition (EVC). However, it is not just a process of identifying the features, such as rock outcrops, vegetation, water features, and so on; you should also try to discern a pattern in the occurrence of these features and their distribution. Some underlying logic generally exists as to why some features occur where they do—rock outcrops are related to geology, erosion, and landform; vegetation to drainage, soil, and exposure; and water features to landform structures and geology. Historic events, such as wildfires, insect attacks, or blowdowns, may have left their mark; and landscape alterations from human activities may be present.

The basic materials required to carry out a landform analysis are panoramic photos, topographic maps, aerial photos, vegetation or forest cover maps, and terrain stability maps. The objective of the landform analysis is to guide cutblock design by identifying visible landscape features in photographs and transferring them to plan-view maps.

For example, identifying the size, shape, and distribution of natural openings on the photograph and on the map can give a designer some insight about the size, shape, and distribution of cutblocks that would work best on the landscape. Describing the type of landforms present (e.g., sharp, rugged peaks), can indicate that sharper, more rugged shapes would best fit the landscape.

Notes:

• Much of the detail to be analyzed can be seen only in the photographs; it will not be obvious on maps.
• Other information can be transferred from the maps to overlays or photocopies of the photographs. Annotations and symbols are useful for this part of the analysis.
• Features beneath the canopy might be revealed after logging. Some of these might help the design, others may suggest places where forest cover needs to be maintained.
• The notes and comments recorded on the plan and perspective views should point out aspects of the pattern and the relationships between different parts of the landscape.

After the land feature analysis is complete, the annotated maps and photographs will provide useful guides to the shape, size, and distribution of cutblocks on the landscape. See step 4 of the "Visual Impact Assessment Procedures" section for information about specific visual design concepts and principles.

Figure A4.2 Landscape feature analysis in perspective and plan view (from the Visual Landscape Design Training Manual, 1994).