Boundaries - some helpful definitions

Boundaries are a topic often discussed online and elsewhere and they can be very complex to understand both in law, registration and the on the ground reality for neighbouring land/property owners.
Many expect HMLR to have all the answers and/or the ability to arbitrate on disputes and more. But the history of land law in England & Wales and how it has developed over the centuries and how land registration has impacted and developed over 160+ years means we very rarely have all the answers and often it comes down to neighbours discussing and sharing information/understanding and agreeing a way forward

Here's a few things to consider when dealing with boundaries
What is the definition of a 'boundary'?
1. Legal boundary - the term is often used to describe the imaginary or invisible line that divides one person’s property from that of another. This could be described as the ‘legal’ boundary. Such a line by definition, has no width and can therefore only be an abstract concept which in practice can rarely be precisely reflected in any form of physical boundary demarcation; and
2. Physical boundary - the term can also be used to describe a ‘physical’ boundary feature which may follow the line of a ‘legal’ boundary. It's demarcation can only be approximate. The degree of imprecision will vary according to the type of boundary feature, and the degree of accuracy to which it is positioned in relation to the ‘invisible’ boundary line.
In considering the problems that may arise relating to boundaries it's always useful to consider the definition of 'land' of ‘land’ in the context of conveyancing. In the ordinary legal sense land includes not only any portion of the earth’s crust and buildings and fixtures standing on it or attached to it, but includes the airspace above and the ground beneath, theoretically to the centre of the earth.
Thus in the legal context, you must consider land as a three dimensional entity, and therefore, horizontal or vertical boundaries may limit the extent of land.
What is the definition of a 'fence'?
he word ‘fence’ can have a wider meaning in the legal sense than that normally used to describe a vertical barrier constructed of wood, metal or concrete, or a combination of these materials. The term may embrace a hedge, ditch, bank or wall, or indeed almost anything constructed to form a physical barrier.
Such a barrier generally serves three purposes:

• to keep trespassers out;
• to keep animals (or people) in; and/or
• o mark a boundary of ownership.

Wooden fences have acquired a fiction which carries little or no legal weight as a presumption, i.e. that the fence belongs to the owner on whose side the post and rails are, or that the nail heads are on the other side from them (the origin of the phrase “to drive a nail home”). Although this may often be the case, the position of posts, rails, nails, etc., is not conclusive evidence as to ownership
The following may also be of interested when considering boundaries
Drawing the line on boundaries
Your property boundaries
Search for land and property information
Boundary agreements and Determined boundaries
As mentioned above many boundary matters can and should be agreed between neighbouring property owners. Far better to reach an agreement than be in dispute but it's crucial to understand that such agreements and determined boundaries rely on BOTH parties and not just one
Unless all the property concerned is unregistered, you can note a boundary agreement in the register.
Boundary agreements tend to focus on the position of the physical feature for example fence or hedge and/or it's maintenance. If the properties are mortgaged then your lender(s) are likely to need to be involved/aware
he agreement is simply noted on each registered title and a copy of deed scanned and filed as appropriate.
Registering a boundary agreement does not alter the registered extent re the 'general boundary'. An application for a Determined Boundary would be required for such an alteration.
A Determined Boundary takes things a step further in many ways.
Unlike a general boundary, a determined boundary shows “the exact line of the boundary of a registered estate”. We don't determine a boundary in the sense of resolving a disagreement as to where the exact line of the boundary is located. Instead, we register the Determined Boundary with the exact line having been identified,
See Practice Guide 40, Supplement 4 Boundary agreements and determined boundaries for more details and the nuances between a boundary agreement and an application for a determined boundary

Please do seek legal advice if you are in a boundary dispute with a neighbour. Whilst there is invariably a reliance on neighbours to resolve such matters there is often misunderstanding as to how the law views such matters.
RICS offer a boundary dispute resolution service which may help resolve any disputes