Route selection is one of the earliest decisions on an onshore pipeline project and one of the hardest to change later. A corridor fixes the length of pipe, the number of crossings, the landowners involved and much of the environmental and planning risk. Geographic information systems (GIS) give engineers a way to compare options on evidence rather than intuition, provided the process is set up properly.
Why route selection deserves a structured method
Traditionally, early routes were sketched on paper maps by experienced engineers and refined by walkover surveys. That knowledge remains valuable, but it is difficult to audit and harder still to explain to planning authorities, landowners and the public. A GIS-led approach makes the reasoning visible: which constraints were considered, how they were weighted, and why one corridor scored better than another.
It also makes iteration cheap. When a new constraint appears, such as a proposed housing allocation or a newly designated site, the analysis can be rerun in hours rather than redrawn over weeks.
Building the constraints dataset
The quality of any routing study depends on its data. A typical onshore study in the UK draws together layers such as:
- Settlements, individual properties and planned development allocations.
- Statutory environmental designations, including Sites of Special Scientific Interest, Special Areas of Conservation and National Parks.
- Ancient woodland, priority habitats and protected species records.
- Scheduled monuments, listed buildings and other heritage assets.
- Flood zones, watercourses and groundwater source protection zones.
- Geology, superficial deposits, mining legacy and landslide susceptibility.
- Roads, railways, canals and existing utilities.
- Terrain data for slopes, ridges and hollows.
Much of this is available from public bodies, though licensing, currency and resolution vary. It is worth recording the source and date of every layer, because constraint data changes and decisions will be revisited months or years later.
From constraints to a cost surface
Classifying constraints
Not all constraints are equal. Most studies sort them into categories along these lines:
- Exclusions, which the route should not cross at all where any alternative exists, such as buildings and certain designated sites.
- High constraints, crossable only with strong justification and specialist techniques.
- Moderate and low constraints, which add cost or risk but are routinely managed.
Weighting and least-cost paths
Each category is given a weighting, and the layers are combined into a single raster cost surface. A least-cost path algorithm then finds the route between two points that accumulates the lowest total cost. Running the analysis with different weightings, for example favouring environmental protection in one run and minimum length in another, shows how sensitive the outcome is to judgement.
The weightings are the most debatable part of the method and should be agreed with the wider project team, including environmental, planning and land specialists, rather than set quietly by the GIS analyst.
Comparing corridors, not single lines
At feasibility stage, it is better to think in corridors a few hundred metres wide than in precise centrelines. Corridors leave room for later adjustments around landowner concerns, ground investigation findings and detailed ecology without restarting the study.
A good comparison scores each corridor against consistent criteria: length, number and type of crossings, proximity to population, area of designated land affected, difficult ground, construction access and likely consenting complexity. Presenting this in a simple matrix, backed by maps, gives decision-makers something they can challenge and defend.
Engineering checks GIS cannot make alone
A least-cost path is a starting point, not a design. Engineers still need to test whether a corridor works physically:
- Crossings. Major rivers, motorways and railways may need horizontal directional drilling, auger boring or microtunnelling. Each needs suitable entry and exit areas and ground conditions.
- Gradients and bends. Steep slopes, sidelong ground and tight changes of direction affect construction method and may require induction bends or special anchoring.
- Proximity and safety. Distances to occupied buildings depend on the product, pressure, diameter and wall thickness, and should be checked against the applicable design code and the project's safety assessment.
- Hydraulics and facilities. Above-ground installations, block valves and compressor or pumping stations need suitable, accessible sites along the corridor.
The product matters too. A dense-phase carbon dioxide line needs particular attention to terrain because releases behave very differently from natural gas, as discussed in our article on designing CO2 pipelines for carbon capture.
Bringing in local knowledge
Desk-based GIS work misses things that are obvious on the ground: a new farm building, field drainage, a private water supply or an access track that cannot take heavy plant. Walkover surveys, early engagement with landowners and consultation with local authorities should feed back into the dataset rather than sitting in separate reports.
Many projects now use shared web maps so that land agents, ecologists and engineers record observations in one place. This keeps the constraints model current and reduces the risk of a late surprise forcing a reroute.
Reuse and parallel routes
Following an existing pipeline or utility corridor can reduce environmental impact and simplify land negotiations, although separation distances and interactions such as cathodic protection interference need assessing. As the UK considers new hydrogen and carbon dioxide networks, the question of whether to build alongside existing gas lines, or to convert them, is becoming central to routing. Our article on repurposing gas pipelines for hydrogen covers the engineering checks involved in conversion.
Practical tips for project teams
- Agree constraint categories and weightings in a workshop, and record the rationale.
- Keep a data register with source, date and licence for every layer.
- Run sensitivity cases and show them to decision-makers, not just the preferred result.
- Carry the GIS model forward into FEED, consenting and construction rather than abandoning it after feasibility.
Done well, GIS-led routing does not replace engineering judgement. It makes that judgement explicit, repeatable and much easier to defend.