The FMB sketch explained: reading your land's map

Land records tell you who holds a piece of land and how much of it there is. But a number like "2.15 hectares" doesn't tell you what the land looks like, where its boundaries run, or who its neighbours are. For that, you need the FMB sketch — the Field Measurement Book sketch, the official survey map of a survey number.

What an FMB sketch is

The FMB sketch is a measured drawing of a survey number prepared and maintained by the survey and land records department. It typically shows:

• Outline of the survey number, drawn to scale
• Subdivisions within it, with their numbers
• Boundary measurements — lengths of each side
• Survey stones or reference points
• Adjoining survey numbers on each side
• Features such as roads, channels or tanks, where relevant

The FMB is part of the system of survey records that underpin all land records in Tamil Nadu.

How to read an FMB sketch

Outline and subdivisions

The sketch shows the overall shape of the survey number and any internal lines dividing it into subdivisions (for example, 123/1, 123/2). Each subdivision corresponds to a separate holding in revenue records.

Measurements

Each boundary line has measurements, recorded in the units used by the survey records. Diagonal or "offset" measurements help fix the shape precisely. A surveyor uses these to locate boundaries on the ground.

Neighbours

Adjoining survey numbers are marked around the edge. This lets you see which parcels border yours — useful for checking boundaries with neighbours and for planning land aggregation.

Survey stones

Survey stones mark boundary points. Over time, stones can be moved, lost or buried. Locating them is part of a boundary survey.

Why the FMB matters

Confirming extent

The area calculated from the FMB should match the extent in the patta and deeds. Differences may reveal errors or unrecorded subdivisions. See what is patta.

Locating the land

The FMB lets a surveyor identify the land on the ground. It is surprisingly common for people to farm land that doesn't exactly match their recorded survey number.

Detecting encroachment

Comparing the FMB with physical boundaries can show encroachment — either onto your land by a neighbour, or onto a neighbour's or government land from yours. See boundary disputes and encroachment.

Project layouts

For solar and wind projects, engineers use surveyed boundaries to design layouts. A layout based on assumed boundaries can end up placing equipment on someone else's land. See solar plant layout basics.

Lease schedules

Lease agreements describe the leased land by survey number, subdivision, extent and boundaries. The FMB supports an accurate schedule.

Using FMBs in land aggregation

When developers assemble a large site from many parcels, they combine FMB sketches into a composite map. This shows:

• How parcels fit together
• Gaps, such as unwilling owners or government land
• Access routes and road frontage
• The usable shape of the combined area

See land aggregation process and pitfalls.

Common FMB issues

• Subdivisions not updated — land sold or partitioned, but the FMB still shows the original survey number. See survey number subdivision records.
• Old or unclear sketches — faded or poorly drawn, needing re-survey
• Mismatch with ground — boundaries on the ground differ from the sketch
• Missing survey stones — hard to fix boundaries without them
• Area differences — FMB area differs from patta or deed extent

Getting a boundary survey

For a significant transaction like a long-term project lease, a boundary survey by a licensed surveyor is often worthwhile:

1. Obtain the current FMB sketch and adjoining FMBs
2. Survey the land and locate survey stones
3. Mark boundaries on the ground
4. Prepare a survey report comparing physical boundaries with records
5. Resolve any differences with neighbours or the revenue authorities

Modern surveys often use GPS and total station instruments, producing coordinates that can be used directly in engineering design.

Digital maps and satellite imagery

Many people now overlay FMB sketches on satellite imagery to visualise land. This is useful for screening, but sketches and imagery may not align perfectly. A field survey remains the reliable way to fix boundaries for a transaction.

Keeping copies on file

Once boundaries have been surveyed and confirmed, keep the FMB sketch, survey report and coordinates together with the patta and deeds. Future transactions, boundary questions and project changes all go faster when the surveyed boundary is already documented.

Common mistakes

• Relying only on extent figures without looking at the shape
• Assuming fences and bunds mark the legal boundary
• Designing project layouts without a boundary survey
• Ignoring small encroachments that grow into disputes
• Using outdated FMB copies

Where we fit

Through land documentation and due diligence and solar land services, we obtain FMB sketches, coordinate boundary surveys with licensed surveyors, and prepare composite maps for multi-parcel sites, so that layouts and lease schedules match the land on the ground.