Category: Land Registry Guides

Ordnance Survey accuracy is a subject that matters to anyone working with Land Registry plans. Every title plan, transfer plan and lease plan submitted to HM Land Registry is based on Ordnance Survey mapping — but that mapping is not a perfect representation of what exists on the ground. There are built-in tolerances at every scale, and understanding them helps explain why boundary positions on title plans are described as “general” rather than exact.

In this guide, we explain how Ordnance Survey accuracy works, what the different map scales mean, how tolerances vary between urban and rural mapping, what relative and absolute accuracy actually measure, and why this matters when you are dealing with property boundaries and Land Registry plans.

Why OS Mapping Is Not Exact

It is not possible for Ordnance Survey to replicate the exact position of every physical feature on the ground. No matter how sophisticated the surveying equipment, there will always be a degree of variation between the real-life position of a feature and where it appears on the map. This variation is known as the accuracy tolerance.

The level of Ordnance Survey accuracy depends on two key factors: the scale of the map and the original survey method used to create it. Urban mapping at 1:1250 scale, which has been surveyed using modern methods, is the most accurate. Rural mapping at 1:2500 and mountain or moorland mapping at 1:10000 have progressively wider tolerances.

This means that if you measure the distance between two features on an Ordnance Survey map and then measure the same distance on the ground, the two figures may not match exactly. The difference will usually be small — especially at larger scales — but it is always present. It is for this reason that HM Land Registry states it is unable to provide scaled measurements from title plans or from Ordnance Survey mapping.

Ordnance Survey Map Scales Explained

Ordnance Survey produces large-scale mapping at three main scales. Each is used for different types of land and has its own level of accuracy.

1:1250 Scale

This is the largest and most detailed OS scale, used for urban areas — towns and cities. At 1:1250, one centimetre on the map represents 12.5 metres on the ground. This is the most common scale for residential and commercial title plans and provides the highest level of Ordnance Survey accuracy.

1:2500 Scale

Used for rural and semi-rural areas. At 1:2500, one centimetre on the map represents 25 metres on the ground. This scale covers farmland, villages and the outskirts of towns. It is less detailed than 1:1250 and has wider accuracy tolerances.

1:10000 Scale

Used for mountain and moorland areas where there is very little built development. At 1:10000, one centimetre on the map represents 100 metres on the ground. This is the least detailed scale and has the widest accuracy tolerances.

The scale of mapping available for a particular property depends on its location. If your property is in a town or city, 1:1250 mapping will be available. If it is in a rural area, you may only have 1:2500 mapping. This directly affects the precision of any Land Registry plan based on that data.

What a Line on the Map Represents

One of the most practical ways to understand Ordnance Survey accuracy is to consider what a single line on the map represents in real-world terms.

• At 1:1250 scale — the width of a line on the map represents approximately 0.3 metres on the ground
• At 1:2500 scale — the width of a line on the map represents approximately 0.6 metres on the ground

This means that even the boundary line itself — before you consider any surveying tolerance — covers a strip of ground rather than a precise point. At 1:2500 scale, the line on the map could represent a strip of land more than half a metre wide. This is one of the fundamental reasons why HM Land Registry operates a “general boundary” rule, meaning the exact line of the boundary is not determined by the title plan.

For property professionals, this is an important reality check. If a client asks exactly where their boundary runs based on the title plan, the honest answer is that the plan shows the general position only — not a precise line on the ground.

The Four Accuracy Categories

Ordnance Survey’s large-scale mapping has been produced at different times using different surveying methods. This means that even maps at the same scale can have different levels of accuracy depending on how and when they were created. There are four accuracy categories.

1. 1:1250 Scale (Urban)

The most accurate category. This mapping covers towns and cities and has been surveyed to the tightest tolerances. Most urban title plans are based on this data.

2. 1:2500 Scale — Resurvey or Reformed

Rural mapping that has been resurveyed using modern methods or “reformed” (redrawn from aerial photography and ground checks). This is reasonably accurate but has wider tolerances than 1:1250.

3. 1:2500 Scale — Overhaul

This is older rural mapping that was originally compiled from pre-1946 County Series maps and updated (“overhauled”) rather than fully resurveyed. It has noticeably wider accuracy tolerances than resurveyed mapping at the same scale. Many rural title plans in England and Wales are still based on overhaul-category data.

4. 1:10000 Scale (Mountain and Moorland)

The least accurate category, covering upland and moorland areas. These maps provide a general picture of the landscape but are not suitable for detailed boundary work.

Relative Accuracy

Ordnance Survey describes accuracy in two ways. The first is relative accuracy — a measure of how accurately the distance between two features on the map reflects the actual distance between those same features on the ground.

Relative accuracy compares scaled distances measured from the map with distances measured on the ground between the same well-defined points. The following table summarises the published relative accuracy values for each mapping category.

What This Means in Practice

At 1:1250 scale, if you measured the distance between two well-defined features that are 60 metres apart on the ground, 95 per cent of those measurements scaled from the map would fall between 59.1 m and 60.9 m. That is a tolerance of less than one metre — highly accurate for mapping purposes, but still not precise enough to determine an exact boundary line.

At 1:2500 resurvey scale, the same exercise over 100 metres would produce scaled measurements between 98.1 m and 101.9 m at 95 per cent confidence. At the overhaul category, the tolerance widens significantly — to ±3.6 m at 95 per cent confidence over 200 metres.

Absolute Accuracy

The second measure is absolute accuracy (also called positional accuracy). This indicates how closely the coordinates of a point on the OS map agree with the true National Grid coordinates of that same point on the ground. Since the “true” position can never be known exactly, absolute accuracy is measured against the best known position determined by precise survey methods.

RMSE stands for Root Mean Squared Error — the standard statistical measure used to quantify the overall accuracy of a dataset. The lower the RMSE value, the more accurate the mapping.

In practical terms, a point shown on 1:1250 urban mapping is expected to be within 0.8 metres of its true National Grid position at 95 per cent confidence. On 1:2500 overhaul mapping, that tolerance widens to 4.7 metres — a significant difference when you are trying to establish the position of a property boundary.

Why Enlarging a Map Does Not Improve Accuracy

A common misunderstanding is that enlarging a map makes it more accurate. It does not. When an Ordnance Survey map is enlarged from its original scale, the degree of accuracy remains the same as the original survey specification.

For example, a plan originally surveyed at 1:2500 and enlarged to 1:1250 will still have the accuracy tolerances of 1:2500 mapping. The features simply appear larger on the page — they do not become more precisely positioned. The underlying data has not changed.

It should also be noted that copying, reducing or enlarging a plan — whether digitally or by photocopying — can introduce further distortion that reduces accuracy beyond the original tolerances. This is one of the reasons HM Land Registry requires plans to be prepared using licensed digital OS data rather than scanned or photocopied maps.

• Enlarging a map does not improve accuracy — the tolerances remain those of the original survey scale, not the enlarged scale
• Photocopying or scanning can introduce distortion — further degrading the accuracy of the plan
• Measurements taken from enlarged plans are unreliable — they carry the tolerances of the original scale plus any distortion from the enlargement process

What This Means for Land Registry Plans

The accuracy limitations of Ordnance Survey mapping have direct implications for every Land Registry plan.

The General Boundary Rule

HM Land Registry operates under the “general boundary” rule. This means that the boundary shown on a title plan indicates the general position of the boundary — not the exact line. The exact boundary between two registered titles is not determined by the title plan unless a specific “determined boundary” application has been made under Section 60 of the Land Registration Act 2002.

No Scaled Measurements From Title Plans

Because of the accuracy tolerances inherent in OS mapping, HM Land Registry cannot provide scaled measurements from title plans. If someone measures a distance from a title plan and assumes it is precise, they may be relying on a figure that is subject to a tolerance of up to several metres — depending on the mapping category.

Why OS-Based Plans Are Still Required

Despite the accuracy limitations, HM Land Registry requires all plans to be based on Ordnance Survey mapping. This is because OS data provides a consistent, nationally referenced framework that allows HMLR to relate every title plan to the same base map. The alternative — allowing plans based on random survey data with no common reference — would make it impossible to maintain a coherent register of title.

What This Means for Property Boundaries

Understanding Ordnance Survey accuracy is particularly important when it comes to property boundaries. The tolerances described above explain why boundary disputes cannot be settled simply by looking at a title plan.

• Title plan boundaries are general, not precise — the line on the plan shows approximately where the boundary lies, not the exact legal boundary
• Small discrepancies are normal — a fence or wall that appears to be slightly inside or outside the boundary line on the plan may simply reflect the accuracy tolerance of the mapping, not an encroachment
• Field measurements should not be compared directly with map measurements — the tolerances mean that a scaled distance from the map and a tape measurement on the ground will rarely match exactly
• Boundary evidence comes from the deeds, not the map — the title plan supports the deed description but does not override it. Physical features, T marks and deed descriptions all contribute to establishing the boundary position

For more information on how Ordnance Survey mapping works, visit the Ordnance Survey website.

How Towers Richardson Can Help

At Towers Richardson, we prepare Land Registry plans using licensed Ordnance Survey MasterMap data — the most current and detailed OS dataset. We understand the accuracy characteristics of the data we work with and ensure every plan meets HM Land Registry standards under Practice Guide 40.

• 100% HMLR acceptance rate — every plan is checked before delivery
• Licensed OS MasterMap data — we work directly with the most current Ordnance Survey dataset
• 30+ years of specialist experience — preparing Land Registry plans since 1994
• Title plans, transfer plans and lease plans — all plan types prepared to HMLR-compliant standards
• Fast turnaround — most plans delivered within 24 to 48 hours, with same-day options available
• Nationwide coverage — we serve clients across England and Wales
• Fixed-price quotes from £115 — no hidden fees, costs confirmed before work starts

Frequently Asked Questions

Need a Land Registry Plan Based on Current OS Data?

Towers Richardson has been preparing Land Registry-compliant plans using licensed Ordnance Survey data since 1994. Whether you need a title plan, transfer plan or lease plan, every drawing is based on current OS MasterMap data and checked against Practice Guide 40 standards before delivery.

We work with solicitors, developers, property professionals and homeowners across England and Wales.

Get in touch today:

📧 info@towers-richardson.co.uk
📞 01226 885040
💬 WhatsApp: 07543 434048

Or request a free quote online — we respond within 1 hour during business hours.

A Land Registry compliant plan is one that meets all of HM Land Registry’s requirements for registration. If a plan does not comply, HMLR will reject the application — raising a requisition that delays the transaction and often requires the plan to be prepared again from scratch.

In this guide, we set out exactly what makes a plan Land Registry compliant, covering the core requirements that apply to all plans, the additional rules for lease plans and complex properties, the common mistakes that lead to rejections, and how you can ensure your plan passes first time. Everything is based on Practice Guide 40 — the official HMLR guidance that governs plan preparation.

What Is a Land Registry Compliant Plan?

A Land Registry compliant plan is a drawing that meets all of the technical and content requirements set by HM Land Registry for property registration. When a plan is compliant, HMLR can use it to identify the land or property being registered, transferred or leased — and the application can proceed without delay.

Compliance is not optional. HMLR will raise a requisition — a formal request for corrections — if a plan fails to meet the required standards. This pauses the application until a corrected or replacement plan is submitted, adding weeks to the transaction and generating additional costs for all parties involved.

The requirements for a Land Registry compliant plan are set out in Practice Guide 40 (and its supplements), which is published by HMLR and updated periodically. Whether you are preparing a title plan for first registration, a transfer plan for a sale of part, or a lease plan for a new lease, the same fundamental standards apply.

Practice Guide 40 — The Standard

Practice Guide 40 is the definitive reference for preparing a Land Registry compliant plan. It is published by HMLR and covers the standards, specifications and requirements that every plan must meet.

The main guide covers the general requirements that apply to all plan types. Supplement 2 provides additional guidance specifically for lease plans, including the requirements for showing demised premises, floor levels and internal layouts.

The key areas covered by Practice Guide 40 include:

• Plan basis — what the plan must be based on (Ordnance Survey mapping)
• Scale — the appropriate scales for different property types
• Orientation — the requirement for a north point
• Content — what must be shown on the plan
• Colouring and marking — how boundaries and areas should be edged, coloured or hatched
• Prohibited content — phrases and features that must not appear on the plan
• Lease plan specifics — additional requirements for plans accompanying leases

You can read the full guide on GOV.UK: Practice Guide 40 and Supplement 2 (Lease Plans).

Core Requirements for All Plans

Every Land Registry compliant plan — regardless of type — must meet the following core requirements.

Based on the Ordnance Survey Map

The plan must be based on current Ordnance Survey mapping and show sufficient OS detail for HMLR to identify the land on the national map. This means surrounding roads, buildings and other features must be visible to provide context. Plans that are not based on OS data — for example, hand-drawn sketches, architect’s drawings or estate agent site plans — will not be accepted.

Drawn to a Stated Metric Scale

The plan must be drawn to a specific metric scale, and that scale must be clearly stated on the plan. The scale must be accurate — if the plan states 1:1250 but the drawing has been resized, HMLR will identify the discrepancy. A scale bar should also be included to allow verification.

Showing Orientation

A north arrow must appear on the plan to confirm its orientation. This is a basic requirement but one that is occasionally overlooked on hastily prepared plans.

Showing Sufficient Detail

The plan must show the whole of the property being registered, transferred or leased, including any associated land such as garden ground, garages, parking spaces, bin stores and access routes. Buildings must be shown in their correct or intended position.

Clear Boundary Marking

The land or property must be clearly identified on the plan. This is typically done by edging the boundary in a continuous colour (usually red for the land being registered or transferred) that forms a complete enclosure with no gaps. Where different areas need to be distinguished — for example, transferred and retained land on a transfer plan — different colours must be used.

Scale Requirements

The scale of a Land Registry compliant plan must be appropriate to the property type and size. Practice Guide 40 specifies the following.

Lease plans for individual flats or units within a building are typically prepared at 1:200 or 1:500 to show the internal layout at a readable size. Title plans and transfer plans for standard residential properties are most commonly prepared at 1:1250 in urban areas and 1:2500 in rural areas.

The scale must be accurate when printed. If a plan is printed at a different size from the original — for example, if an A3 plan is printed on A4 paper — the scale will be wrong and the plan will not be compliant.

Colouring and Marking

A Land Registry compliant plan must use colour and marking to clearly identify the land or property. The conventions vary depending on the plan type, but the general principles are consistent.

Title Plans and First Registration

The boundary of the property is edged in red, forming a complete enclosure. The edging must be clearly visible and must not obscure the detail beneath it.

Transfer Plans (TP1/TP2)

The land being transferred is edged in red. The retained land is edged in blue. Any rights of way or easements are shown in a different colour — typically brown for access routes and green for communal areas.

Lease Plans

The demised premises (the area being leased) are typically edged in red or shown with a coloured wash. Communal areas are shown in a different colour, and any rights over other parts of the building (such as access routes or shared facilities) are identified using additional colours or hatching.

In all cases, the colours must be clearly distinguishable from each other and from the base OS detail when printed. Colours that merge or become ambiguous on paper will result in a requisition from HMLR.

Additional Requirements for Lease Plans

Lease plans have additional requirements beyond the core standards. These are set out in Practice Guide 40 Supplement 2 and reflect the fact that leases often cover complex three-dimensional spaces within buildings rather than simple parcels of land.

A Land Registry compliant plan for a lease must meet all of the core requirements and the following additional standards.

• Relationship to the building footprint — the plan must show where the demised premises sit in relation to the external footprint of the building and the surrounding detail on the Ordnance Survey map
• Floor-level plans — if the lease covers property on more than one floor, or if the extent of the demise varies by floor, separate plans must be provided for each level
• Subsoil and airspace — if the lease includes land below or above ground level (for example, a basement or an upper-floor flat), the plan must show the relevant levels, ideally referenced to Ordnance Survey Datum
• Intricate boundaries — internal divisions within a building, such as party walls between flats, must be shown clearly so that the exact extent of the demise can be identified
• Communal areas — shared spaces such as hallways, stairwells, lifts and bin stores must be shown and distinguished from the demised premises
• Access routes — the routes by which the tenant accesses the demised premises from the building entrance should be identifiable on the plan

Prohibited Phrases and Common Errors

Certain phrases and features will cause a plan to fail compliance, regardless of how well it is drawn. These are the most common errors that result in HMLR rejections.

Prohibited Phrases

The following phrases must never appear on a Land Registry compliant plan:

• “Not to scale” — if the plan is not to scale, it cannot be used for Land Registry purposes
• “For identification purposes only” — this implies the plan is approximate, which undermines its value for registration
• “For illustrative purposes only” — same principle as above
• “Do not scale from this drawing” — contradicts the requirement for a stated, accurate scale
• “Subject to survey” — suggests the plan may change, which is not acceptable for a definitive registration document
• “Approximate boundary” — all boundaries on a registration plan must be shown as definitively as the OS data allows

Other Common Errors

• Boundary edging with gaps — the red (or other) edging must form a complete enclosure with no breaks
• No north arrow — a basic omission that still causes rejections
• Missing scale bar — the scale must be stated and verifiable
• Insufficient surrounding detail — the plan must show enough context (roads, buildings, features) for HMLR to locate it on the OS map
• Inconsistency with the deed — the plan must match the verbal description in the transfer, lease or other document it accompanies
• Plan not based on OS data — architect’s drawings, estate agent plans and builder’s site plans are not acceptable without an OS base
• Scale distorted by printing — if an A3 plan is printed at A4 size, the scale changes and the plan is no longer compliant

Requirements by Plan Type

While the core requirements are the same, each plan type has specific considerations that affect compliance.

Compliance Checklist

Before submitting any plan to HM Land Registry, check it against this compliance checklist. Every item must be satisfied for the plan to be accepted.

• Based on current Ordnance Survey mapping — licensed OS data, not a sketch or architect’s drawing
• Drawn to a stated metric scale — clearly printed on the plan with a scale bar
• Scale is accurate when printed — check by measuring the scale bar with a ruler
• North arrow present — confirming the orientation of the plan
• Sufficient surrounding detail — roads, buildings and features visible for context
• The whole property is shown — including gardens, garages, parking, access routes
• Buildings in correct position — matching the OS mapping or shown in intended position for new builds
• Boundaries form a complete enclosure — no gaps in the red (or other colour) edging
• Colours are clear and distinguishable — will remain readable when printed
• No prohibited phrases appear — no “not to scale,” “for identification only” or similar
• Plan matches the deed description — the visual and verbal descriptions are consistent
• Lease plan specifics met — floor plans, building footprint relationship, communal areas (if applicable)
• Date of preparation included — a record of when the plan was produced

How Towers Richardson Can Help

Preparing a Land Registry compliant plan requires specialist knowledge of Practice Guide 40, access to licensed Ordnance Survey data, and professional CAD software. At Towers Richardson, we bring all three together — along with over 30 years of experience producing plans that HMLR accepts first time.

• 100% HMLR acceptance rate — every plan checked against Practice Guide 40
• Licensed Ordnance Survey data — we work directly with current OS MasterMap
• Title plans, transfer plans, lease plans and developer plans — all plan types prepared to the same compliant standard
• 30+ years of specialist experience — preparing Land Registry plans since 1994
• Fast turnaround — most plans delivered within 24 to 48 hours, with same-day options available
• Nationwide coverage — we serve clients across England and Wales
• Fixed-price quotes from £115 — no hidden fees, costs confirmed before work starts

If you have had a plan rejected and need a compliant replacement, we can typically deliver within 24 hours. Contact us with the details and we will provide a fixed-price quote.

Frequently Asked Questions

Need a Compliant Plan?

Towers Richardson has been preparing Land Registry compliant plans since 1994. Whether you need a title plan, transfer plan, lease plan or developer plan, every drawing is prepared to Practice Guide 40 standards and checked before delivery.

We work with solicitors, developers, estate agents and property professionals across England and Wales.

Get in touch today:

📧 info@towers-richardson.co.uk
📞 01226 885040
💬 WhatsApp: 07543 434048

Or request a free quote online — we respond within 1 hour during business hours.