Linear Corridor Surveys

Linear corridor surveys cover elongated routes rather than discrete areas — road corridors, pipeline easements, fibre optic routes, transmission line clearances, and rail corridors. They are common in Australian environmental consulting, particularly for EIA (Environmental Impact Assessment) work where the project footprint follows a linear alignment rather than a bounded site.

What is a corridor survey?

A corridor survey uses a centreline route measured in kilometres instead of a polygon area measured in hectares. The corridor is defined by:

• Centreline — the route itself (e.g., a proposed road alignment or pipeline path)
• Buffer width — the distance from the centreline to the corridor edge (e.g., 30 m each side = 60 m total corridor width)

Typical corridor widths:

• Road EIA corridors: 50–100 m each side
• Pipeline easements: 25–50 m each side
• Fibre/utilities: 10–30 m each side
• Transmission lines: 50–150 m each side

Setting up a corridor quote

1. Open a quote and navigate to the Site Boundary panel.
2. Click the Linear Corridor toggle (next to "Area Survey") at the top of the panel.
3. Define the centreline using one of two methods:
   • Draw — Click "Draw" then click points along the route on the map. Double-click to finish.
   • Import GIS — Click "Import GIS" and upload a GeoJSON or KML file containing a LineString geometry.
4. Once a centreline is drawn, set the Buffer width (distance in metres from centreline to corridor edge). The map will preview the full corridor footprint as a shaded polygon.

The panel displays the corridor length in kilometres and the derived area in hectares based on the centreline length and buffer width.

How estimation differs from area surveys

Corridor surveys use per-kilometre estimation rather than per-hectare:

• Field day calculation — Based on corridor length (km) and corridor width, not site area alone.
• Transect method — Creates parallel passes along the corridor (running parallel to the centreline) rather than perpendicular transects across the site. The number of passes is determined by corridor width ÷ offset spacing.
• Offset spacing — For corridor transects, the "Spacing" field becomes "Offset spacing" — the distance between each parallel pass. A 60 m wide corridor (30 m buffer) with 20 m offset spacing generates 3 parallel passes.
• Interval — Not applicable to corridor transects. The Interval field is hidden when a corridor site type is active.

Intelligence factors for corridors

The Smart Estimate panel adapts its intelligence factors for corridor geometry:

• Scale — Measured in kilometres of corridor rather than hectares. Longer corridors increase base effort proportionally.
• Shape (Sinuosity) — Measures how winding the route is. A highly sinuous corridor (e.g., following a creek) takes longer to traverse than a straight alignment of the same length.
• Road Access — Counts access points along the corridor route (e.g., road crossings, easement gates) rather than measuring distance from a single centroid to the nearest road. More access points generally reduce repositioning time.
• Terrain and Vegetation — Applied per kilometre of corridor rather than per hectare of area.

Travel analysis for corridors

The travel analysis identifies the nearest TerraSitu office to any point on the route, not just the corridor centre. For long corridors spanning hundreds of kilometres, the system may identify multiple offices as relevant staging points.

Repositioning time (moving between access points along the route) is estimated based on corridor length and the number of identified access points.

Mixed projects

A single project can contain both corridor sites and area sites. For example:

• A pipeline route assessed as a linear corridor
• A detailed polygon assessment at a creek crossing or sensitive heritage site along the route

Each site is quoted independently with the appropriate geometry type. The quote line items from both sites combine into a single project total.

When working with mixed projects, use the site type toggle in the Site Boundary panel to select the correct geometry for each site.