Title plans, aerial photos and measurements: draw your plot without getting the boundary wrong

You want to put a shed 2 m from the boundary, check that a pool fits in the garden or draw the path to the gate. It all starts with the same question: where exactly is the boundary of the plot, and what are its dimensions?

Three sources are within reach: the title plan, the aerial photo and your own measurements. A fourth, a land surveyor's plan, is the most reliable when it exists. Each has its flaws. The point of this guide is to know which, so you use the right source for each question.

The title plan: what it says and what it doesn't

In England and Wales, HM Land Registry keeps a title register and a title plan for registered land, which covers most property sold since 1993. The plan shows the extent of the land, edged in red, on Ordnance Survey mapping. At the time of writing, gov.uk sells an online copy of the title plan for £7, and an official copy for £11. Elsewhere, the equivalents are Registers of Scotland, Land & Property Services in Northern Ireland, and Tailte Éireann in Ireland, whose map you can search on landdirect.ie. In the US, the county assessor's parcel map plays a similar role, with the same limits.

What the title plan doesn't do:

• It doesn't show the exact legal boundary. HM Land Registry says most titles show only general boundaries, and that there's no standard tolerance between the red line and the real legal line. Tailte Éireann describes its map in the same spirit: it identifies property, not boundaries.
• It isn't precise at garden scale. A red line drawn on a small-scale map can be a metre or more wide on the ground. Scaling a distance off it gives an order of magnitude, not a measurement.
• It isn't always up to date. A recent extension, a shed or a plot split may be missing from the base map.
• An area worked out from it isn't a survey. For a sale or a dispute, what counts is the deeds and any surveyed plan.

It's still very useful for the overall shape of the plot, its angles, its orientation and where the neighbours are.

The surveyor's plan: the reference

If you have a measured survey by a land surveyor, a plan attached to the transfer when the plot was split off, or a set-out drawing from a recent build, that's your best source for the boundaries. It gives measured dimensions, sometimes coordinates, and the position of fixed points.

Look in the purchase documents, ask your conveyancer, or ask the seller. For a project close to the boundary, such as a shed, a carport or an extension, a boundary survey costs less than a dispute with the neighbour. In England and Wales, an exact line can even be recorded at HM Land Registry as a determined boundary, which usually needs the neighbour's agreement and a surveyor's plan.

The aerial photo: a photo to scale, with its traps

An orthophoto is an aerial photo corrected and tied to coordinates: each pixel matches a known area on the ground. That's what lets you draw straight on top of it to scale.

In the UK and Ireland, Architektor uses Esri's satellite imagery. You type your address, choose the level of detail, and the image goes down at real scale. The editor shows the resolution, in centimetres per pixel, and lowers the level of detail by itself where the imagery runs out. Official orthophotos are built in only for Belgium (Wallonia, Flanders and Brussels).

National mapping agencies publish their own imagery and mapping: Ordnance Survey in Great Britain, Tailte Éireann in Ireland, the USGS in the US. They aren't built into Architektor. You can take a screenshot, import it like a plan and calibrate it (see below), as long as you respect their terms of use: many products are licensed, not free.

The traps to know about:

• The roof overhang. From the sky you see the roof, not the walls. A house with a 50 cm overhang looks 1 m wider and longer than it is.
• Leaning buildings. Except on so-called true orthophotos, a roof is slightly offset from the foot of the walls, all the more so when the building is tall and far from the centre of the shot.
• Trees and shadows hide fences and distort outlines.
• The date of the photo. A hedge pulled out or a shed built after the picture was taken won't be there.

The right way to use the aerial photo: to place things (the house on the plot, the trees, the path), not to size them. The dimensions come from your measurements or the surveyor.

Measure it yourself

For the house, the guide draw a floor plan of your house covers the method. For the plot, a few techniques are enough:

• Measure horizontally. On sloping ground, a tape laid on the ground gives a length that's too long. Hold it level, in sections if needed. A laser measure works in a straight line, but it needs something to aim at.
• Triangulate what you can't line up. To place a tree, measure its distance from two corners of the house: say 7.20 m from the north-east corner and 9.80 m from the south-east corner. Only one point in the garden matches both distances.
• Check right angles with the 3-4-5 rule: 3 m along one side, 4 m along the other, and the diagonal should be 5 m. With 6, 8 and 10 m, it's more precise.
• Start from fixed points when you have them: a surveyor's marker, an old boundary wall, a fence post that everyone agrees on. A survey marker is often a small peg, pin or plate, sometimes buried a few centimetres down at the foot of a fence.
• Don't trust your phone's GPS for a boundary: an error of several metres is normal.

Example. At a scale of 1:1250, the title plan suggests a back boundary of about 15 m. You measure 14.62 m between the two corner fence posts. Both are plausible: the fence may not be on the boundary, or the red line is simply too coarse to tell. Without a surveyor's plan, draw what you measured, write “title plan: about 15 m” in the Notes field, and keep the question open for any project close to the boundary.

Calibrate an imported plan

A title plan, a surveyor's plan, an architect's drawing or a screenshot of aerial imagery can be scaled in two clicks in Architektor:

1. Import the document: an image (JPG, PNG) or a PDF, from the base maps.
2. Click two points whose real distance you know, then type that distance. The image is scaled.
3. Adjust the position and rotation: unlock the base map to move it with the mouse, and set its rotation in degrees to line it up with the house or the aerial photo. Lower its opacity to see what's underneath.
4. Check a third dimension with the Measure tool (M key). If it's out by more than a few centimetres, start again with other points.

The choice of the two points makes all the difference. Pick them as far apart as possible. A 2-pixel click error over 200 pixels is a 1% error, so 30 cm across a 30 m plot. Over 1,000 pixels, the same error is only 6 cm.

A few traps:

• The printed scale (“1:1250”) means nothing once the plan has been scanned or printed with “fit to page”. Calibrate on a written dimension or on the document's scale bar, never on the scale written on it.
• A phone photo of a plan, even well framed, is distorted by perspective. Scan it, or photograph it perfectly flat and square on.
• A scan can be slightly stretched in one direction. Check one dimension in each direction.

Combine the sources on your plan

In practice, you layer everything:

1. The aerial photo as the base, to put the house and the plot in context.
2. The title plan or the surveyor's plan, imported and calibrated, with its opacity turned down.
3. The plot boundary, drawn with the Area tool set to “Plot boundary”, following the surveyor's plan where you have one, otherwise the title plan corrected by your measurements. The area is shown in m² and in ares.
4. The house, drawn from your measurements, then placed on the photo by lining up the foot of the walls, not the edge of the roof.

Note the source of each boundary in the Notes field: “boundary survey 2019”, “title plan”, “fence measured”. The day you plan a shed or a carport 2 m from the boundary, you'll know how far to trust that line. For the next step, the guide draw a garden plan to scale starts from exactly this survey.