Understanding the Tree Horizon Line
When you begin your site, you’ll first draw your red line boundary. This shows the exact area of your land — your site.
However, most Local Planning Authorities (LPAs) are not only interested in trees inside your boundary. They also want to know about any trees outside your site that could be affected by your development, or that might affect your plans (for example, large trees whose roots or canopy spread across the boundary).
You’ll notice this same rule is reflected in the Planning Portal question about trees — it asks whether there are any trees on or near the site that could be influenced by the proposed works.
To make this easy, we use something called the Tree Horizon Line.
The Tree Horizon Line defines the wider area where you should record trees for your assessment. Every LPA has slightly different requirements, but in most cases this area will include:
Your red line site boundary; and
An additional 15 metres around the proposed development area.
This helps make sure you capture all trees that could be affected — whether by root spread, canopy overhang, felling, or pruning. It also ensures trees that fall within potential falling distance are included.
On this page, you’ll see your Tree Horizon Line displayed on the map.
If you believe a different area would be more appropriate, you can adjust it using the Advanced Tools option on the right.
However, we strongly recommend keeping the default Tree Horizon Line unless you have a clear reason to change it. It’s designed to meet the requirements of most LPAs and to make your application process as smooth as possible.