How to Scan a Large Document With a Phone in Sections

To scan a large document with a phone, do not try to fit the whole sheet into one readable picture. Take one overview photo for reference, then photograph the sheet in overlapping sections, each about the size of a letter page, in a fixed order. Keep every section photo and label the set.

A phone camera has a fixed number of pixels. Spread them over a survey plat or a set of building plans and the lot dimensions, bearings and notes shrink to a few dots each. Sections solve that, at the price of some planning. This post gives the arithmetic, the shooting pattern and the point at which a phone is the wrong tool.

Can a phone scan a document larger than letter size?

Yes. A phone can capture a sheet of any size if you treat the camera's pixels as a budget and spend them on one section at a time. One frame covers roughly a letter-size area at a density that keeps ordinary print readable. A bigger sheet needs more frames, not a longer step back.

Think of each photo as a fixed grid of pixels. Fill the frame with a letter page and every inch of paper gets a generous share. Fill the same frame with a sheet three feet wide and every inch gets about a third of that share along each side. The picture still looks sharp as a thumbnail, because the drawing's lines are bold. The six-point lettering beside those lines is what fails.

The sum that links megapixels, distance and print size belongs to the post on how many megapixels a phone needs to scan a document. The working rule for an oversized sheet is simpler and you can test it on the spot:

1. Find the smallest lettering on the sheet. On a plat that may be a bearing along a lot line or a recording note. On a drawing it may be a dimension or a revision entry.
2. Photograph the area around it from a height where about eleven inches of paper fills the long side of the frame.
3. Zoom in on the photo. If you can read the small lettering without guessing, that height is your working distance. If not, move closer and try again with a smaller patch.

The patch of paper one frame covers at your working distance is your tile. Everything else follows from its size.

How many photos does a large sheet need?

Count the tiles along each side of the sheet and multiply. With a tile about 11 by 8.5 inches and an overlap of 1.5 inches between neighbors, an 11 by 17 sheet takes 3 photos, an 18 by 24 sheet takes 8, and a 24 by 36 sheet takes 15, plus one overview.

The arithmetic

Each new tile moves you forward by the tile's length minus the overlap. So along one side of the sheet:

tiles along a side = (side length − overlap) ÷ (tile length − overlap), rounded up

Do that for the width and the height, then multiply the two numbers. Try the tile both ways round, long side across and long side down, and use whichever gives fewer photos.

Worked figures

These assume a tile of 11 by 8.5 inches and a 1.5 inch overlap. Measure your own sheet with a tape before you rely on a size printed in a title block.

Take the third row as a check. The sheet is 36 inches wide. With the tile's short side across, each step is 8.5 minus 1.5, or 7 inches. Thirty-six minus 1.5 is 34.5, and 34.5 divided by 7 is 4.9, so five columns. Down the 24 inch side each step is 11 minus 1.5, or 9.5 inches. Twenty-four minus 1.5 is 22.5, and 22.5 divided by 9.5 is 2.4, so three rows. Five times three is fifteen.

When the tile can be bigger or must be smaller

The tile size is set by the smallest lettering, not by the sheet. A subdivision plat with bold lot numbers and nothing smaller than typewriter size may read well with a tile twice the area, which halves the count. A drawing with fine dimension strings may need a tile half the area, which doubles it. Photograph a patch of your sheet's smallest lettering, read it at full zoom, and put the tile size that passes into the formula.

Add the overview photo to the total, and add one close photo each for the title block, the legend, the scale bar and any certificate or seal. Those are the parts people cite, so they deserve a frame to themselves.

When the sheet is a plat attached to a client's lease, keep every section photograph plus the overview. The set can serve as documentary evidence of the drawing, and the overview helps authentication by showing how the tiles fit. Name the files by row and column so the chain of custody of the capture stays in order.

Shooting an oversized sheet in overlapping tiles

Shoot the tiles in rows, left to right and top to bottom, from the same height, with the phone flat over the center of each tile and a strip of shared paper between neighbors. Photograph the whole sheet first, and write the row and column count down before you start.

Setting up

• Flatten the sheet. A rolled drawing wants to curl. Lay it on a large table or a clean floor and weight the corners with something that sits outside the drawn area. Do not crease or tape an original without permission from whoever holds it.
• Find even light. A sheet this size picks up your shadow and the shadow of the phone. Stand so the main light comes from the side, or use a room with several ceiling lights. Turn the flash off.
• Put a ruler on the sheet. A tape measure or ruler lying along one edge, inside the overview photo, lets a reader judge size later.
• Mark the grid lightly, off the paper. Slips of paper along the table edge, numbered 1 to 5 across and lettered A to C down, tell you where each tile's center is. Nothing should be written on the document.

The sequence

1. Overview. One photo of the whole sheet, taken from as high as you can manage with the camera level. Its job is to show where every tile sits.
2. Row A, left to right. Hold the phone at your working height, flat, over the center of tile A1. Take the photo. Step sideways and repeat for A2, keeping a strip of A1 in the frame.
3. Row B, left to right. Start again at the left side. Starting each row from the same side keeps the camera roll in a predictable order.
4. Remaining rows. Same pattern until the bottom edge.
5. Detail shots. Title block, legend, scale, north arrow, signatures, seals, recording stamps, revision table.
6. Review before the sheet is rolled up. Count the photos against the grid. Open each at full zoom and read the smallest lettering near every edge.

Why overlap matters

The overlap does two jobs. It guarantees that a label lying on the boundary between two tiles appears whole in one or both of them. And it gives anyone looking at the set a shared feature, such as a lot corner or a grid line, to prove two tiles are neighbors. An inch and a half covers a short label. Use more if the sheet has long labels running across where a boundary would fall.

Keeping the camera square

Moving the phone sideways, not pivoting it from one spot, is what keeps the tiles consistent. A phone tipped toward a far corner photographs that corner at a slant, and the lettering there comes out smaller and softer. If the sheet is pinned to a wall instead, the same sideways-step pattern applies, and the post on taking a picture of a whiteboard covers standing position and reflections for wall-mounted surfaces.

Legal-size pages and long scrolls of paper

A legal-size page fits one frame if its print is ordinary size, at about four-fifths of the density a letter page would get. Check the small print and split the page into two overlapping halves if it is soft. A long strip of paper is shot as a single row of tiles from one end to the other.

Legal size, 8.5 by 14 inches

The long side of a legal page is 14 inches against 11 for letter. Fill the frame with it and each inch of paper gets 11/14 of the pixels, a loss of roughly a fifth. For a typed lease or a court form in normal type that is fine. For a closing statement or a form with dense fine print, take two photos, top half and bottom half, with a couple of inches shared in the middle.

Two more things go wrong with legal pages on a phone. A scanning app's crop outline can stop short of the foot of a long page and trim the bottom lines. And if you frame by habit for letter proportions, the foot of the page can fall outside the picture. Look at the last line of the paper and the last line of the image side by side. The post on scanning legal-size documents deals with text cut off at the edge of a page in more detail.

Ledger and tabloid, 11 by 17 inches

An 11 by 17 sheet is two letter pages side by side. Spreadsheets printed large, organization charts and site plans can arrive on it. Two tiles with no shared strip leave you exposed at the boundary, so allow three with an overlap. If the sheet is a printed table, set the tile boundaries between columns or rows where you can, so that no cell is split.

Strips and scrolls

Adding-machine tapes, continuous printouts, monitor strips and long receipts are narrow and very long. Treat them as one row:

1. Unroll a section and hold it flat with weights at both sides.
2. Lay a ruler or tape measure beside the strip so its numbers show in every photo. The ruler readings then prove the order and the overlap.
3. Photograph, slide the strip along by one tile less the overlap, and repeat.
4. Finish with a photo of each end, so it is clear nothing continues beyond.

Thermal paper fades, so do not leave a strip under a hot lamp while you work out the pattern.

Should tiles of a large document be stitched before OCR?

Convert the tiles separately and keep them as the record. Stitch only if someone needs a single picture to look at, and label that picture as a composite. A stitched image can hide a doubled or missing strip at a seam, and it may be too large to upload without being shrunk.

What each route gives you

On a plat or a drawing, the text is scattered labels, not running prose, so losing the flow between tiles costs little. What you want from recognition there is the ability to search for a lot number, a street name or a note, and separate tiles give you that. Duplicate hits from the overlap are harmless once you know to expect them.

A printed table or a page of dense notes is different. If a boundary cuts through it, re-shoot that area as a single tile centered on the table instead of stitching two halves.

Putting the tiles through a converter

Combine the tiles into one PDF in shooting order, overview first, so the set travels as one document with page numbers. A set of fifteen full-size photos is heavy, so check the file against the upload limit before you send it. Schema Law takes PDF, PNG and JPEG files up to 20 MB, reads each page into text, and lets you export the result in any of its eight formats. Split a heavy set into two PDFs by row; do not lower the image quality to make it fit. The how it works section shows the upload steps.

Do not expect the output to resemble the drawing. Recognition returns the words it finds. Line work, symbols and the position of a label beside the thing it names are not part of the text. The post on OCR for contract exhibits covers site plans and drawings attached to agreements, and what to do with exhibits that are mostly picture.

If you stitch anyway

Panorama modes in phone cameras are built for a scene swept from one standing point, and sweeping one over flat paper can bend straight lines. Assembling the tiles in image software on a computer gives you control of each seam. Either way, name the file as a composite, keep it beside the tiles, and never let it replace them. Read across every seam and compare with the paper or the tiles for anything doubled or missing.

When a plat or drawing should go to a large-format scanner instead

Send the sheet to a large-format scanner when someone will measure from the image, when the lettering stays unreadable at full zoom however small you make each section, when there are many sheets, or when a court, recorder or agency will receive the copy. A phone set is a working copy. It is not a scaled reproduction.

Signs you have reached the phone's limit

• Scale matters. A scanner feeds the sheet past a fixed sensor and holds one scale across the whole image. Phone tiles each have their own slight tilt and distance. Nobody should scale a boundary or a setback off a phone photo.
• Small lettering will not resolve. If the smallest lettering is unreadable until the tile is the size of a postcard, the photo count for a full sheet runs into the dozens and the chance of a gap rises with it.
• There is a set, not a sheet. Fifteen photos for one plan is tolerable. A forty-sheet construction set is six hundred.
• The copy is going to be filed or recorded. Recording offices and courts set their own requirements for size, legibility and format. Read the requirements that apply to you before you decide how to capture the sheet.
• The original is fragile or valuable. Repeated handling on a floor is a risk to an old linen or mylar original.

Better sources than a scan of any kind

Before paying for a scan, ask whether a digital original exists. A drawing produced in design software can be exported to PDF by the firm that drew it, with real text and exact scale. A recorded plat may be available as an image from the office that recorded it. A copy obtained that way saves the capture step entirely and comes with a clearer account of where it came from.

Using the phone set in the meantime

If a proper scan will take days, the phone tiles still earn their keep. They let you read the notes, search the labels after conversion, and brief the person who will order the scan on which sheets matter. File them with a short note that says who photographed the sheet, where, on what date, how many tiles there are and in what order. Recognition is strongest on clean print, and nothing in the output marks a doubtful word, so check any lot number, dimension or bearing you intend to quote against the tile it came from. Page limits for longer sets are on the pricing page.