Visual Impact Assessment Guidebook

Table of Contents

Appendix 7

Sight line plotting instructions and presentation criteria

Sight lines

• Using the best topographic map scale available, plot sight lines to determine the areas visible from each viewpoint. Sight-line plots determine the extent of visible alteration(s) from viewpoints; the sight-line map (topographic map) shows the direction of lines of sight from the same viewpoints.
• Based on the sight-line plots, indicate on the topographic map the portion(s) of the proposal(s) that would be visible.
• Plot sight lines (also called "topographic sections or profiles") using the best scale available (preferably at 1:10 000 or larger) from each important viewpoint.
• Label each sight-line plot with the viewpoint number, opening number, sight line number, and scale of the topographic map used for the plotting.
• Provide an elevation bar on the upslope end of the profile and a distance scale on the horizontal bar (see the following example).
• Identify the start and end of the opening with a tree representative of stand height class (see Figure A7.1).
• Indicate road locations within the block.
• Shade in the visible area and transfer these data onto the topographic map.
• Minimize vertical exaggeration; the recommended vertical exaggeration is 1:1–1:1.5.

Figure A7.1 Plotting a sight line.

Making topographic sections from a contour map. (a) Draw line of section on map from viewpoint across the relevant part of the terrain. Project lines at right angles from where the line of section cuts the contour to the corresponding heights on the sectional drawing above. (b) Connect the points on the section and draw line(s) of sight from the viewpoint. (c) Illustrate tree heights at appropriate age intervals as required.