Drawing Markup Symbols Explained: Clouds, Deltas, Crossouts & More

Short answer: Drawing markup symbols are the visual shorthand reviewers use to flag changes and corrections on construction drawings. The most common are the revision cloud (encircles a changed area), the revision delta or triangle (a numbered tag that ties a change to a revision table), the crossout or strikethrough (deletes something), the leader or arrow (points a comment at a specific spot), and the callout bubble (links a detail to where it is drawn). Each is a question or instruction aimed at someone. Archi Check produces these same symbols as tracked comments, so every cloud, arrow, and callout carries an owner and a status instead of sitting as static ink.

Open any marked-up drawing and you are reading a language. A loop of cloud here, a small numbered triangle there, a line struck through a dimension, an arrow trailing a note into the margin — none of it is decoration. Each mark is a reviewer telling someone else that something needs attention, and each carries an implied instruction: change this, check this, delete this, explain this. The trouble is that the language is learned on the job, rarely written down, and inconsistent from one office to the next.

This guide is a reference. It sets out the markup symbols you will actually meet on architectural and construction drawings, what each one means, and how reviewers use them in practice. Treat it as a glossary you can return to, and as a way to make sure your own markups say what you intend them to say.

What "drawing markup symbols" actually means

A markup symbol is any mark added on top of a drawing after it was authored, to communicate a change, a question, or a correction. Markups sit in a layer above the drawing itself — historically in red pen over a print, today usually as digital annotations over a PDF or in QC software. The drawing underneath is the design; the markup is the conversation about it.

Two families of symbol get bundled under the term, and it helps to keep them apart. The first is revision symbols: clouds and deltas that formally record that a published drawing has changed between issues. These belong to document control and usually end up baked into the drawing's revision history. The second is review markups: the arrows, crossouts, callouts, and notes a checker adds during a quality check, before anything is reissued. These are working comments — they are meant to be acted on and then cleared.

The same shape can appear in both families, which is where confusion starts. A cloud drawn during a review says "look here, this is wrong." The same cloud, once the change is published, says "this area changed in revision C." Knowing which conversation you are in tells you what the mark is asking of you.

The markup symbol reference table

This is the quick-reference version. Each symbol is covered in more depth in the sections that follow, but the table is the part to bookmark — it maps each common mark to what it means and what the reviewer expects you to do about it.

Revision symbols: clouds and deltas

Revision symbols are the most formal markup family because they survive into the published drawing. They exist to answer one question for anyone holding a sheet: what changed, and when.

The revision cloud

A revision cloud is a closed loop of small arcs — it looks like a child's drawing of a cloud — wrapped around the part of the drawing that has changed. Its only job is to direct attention. Rather than make the reader compare two versions of a dense sheet line by line, the cloud says "the change is inside here." During a review, a checker uses the same shape to ring an area that needs correcting, which is why clouds appear both as working markups and as published revision records.

There is a convention worth knowing about how clouds accumulate. The cloud method usually shows only the changes from the most recent revision; previous clouds are removed as their changes are absorbed, so the sheet does not silt up. That keeps each issue legible but means a single sheet does not, by itself, show its full change history — the revision table does that.

The revision delta (triangle)

The delta is a small triangle — the Greek letter delta, used in engineering to mean "change" — usually containing a number or letter. It is the index that makes a cloud traceable. A cloud says "something here changed"; the delta beside it says "this is change number 3," and number 3 has a row in the revision table giving the date, a description, and who authorised it. Unlike clouds, deltas often stay on the sheet across issues, so the triangles accumulate as a visible record of every revision the drawing has been through.

The pairing matters. A cloud with no delta is a change nobody can look up; a delta with no cloud is a record with no location. Used together — the cloud-with-tag in the reference table — they make a change both visible on the sheet and findable in the register.

Review markups: arrows, crossouts, callouts, and notes

Where revision symbols record history, review markups drive the present conversation. These are the marks a checker adds during a quality check, each one a small instruction meant to be acted on and then cleared.

Leaders and arrows

A leader is a line, usually with an arrowhead, that connects a comment to the exact element it concerns. It is the most basic and most important markup, because it removes ambiguity about location. "This door swing is wrong" floating in white space could mean any of six doors; the same note with an arrow touching one door leaf is unmistakable. Good reviewers anchor almost every comment with a leader for this reason — the arrow is what turns a vague observation into an actionable one.

Crossouts and strikethroughs

A crossout is a line drawn through something — a note, a dimension, a label, an element — to mark it for removal or replacement. On its own a strikethrough says "delete this." Paired with a replacement written alongside, it says "this is wrong, use this instead," which is the most common form on dimension and text corrections. The discipline that makes crossouts safe is always supplying the intended value rather than only deleting the wrong one, so the corrector is not left guessing.

Callout bubbles

A callout bubble is a circle or oval that cross-references parts of a drawing set — most often tying a plan to an enlarged detail or a section. The bubble typically carries a detail number over a sheet number, telling the reader where to find the related view. As a review markup, a callout flag points out that a reference is missing, wrong, or pointing at the wrong sheet, which is one of the more common coordination defects in a large set.

Text notes and comments

Not every markup is a symbol. Much of the substance of a review is plain text — a note explaining what is wrong, a question to the design team, a reference to a code clause. Text on its own is weak because it floats; the strong pattern is text anchored by a leader to the element it describes, so the comment and its location travel together.

Corrections: dimensions, hatches, and highlights

Some markups are less about pointing and more about fixing a specific class of error. These show up constantly in architectural QC.

Dimension corrections

A dimension correction is a crossout aimed specifically at a measurement: the wrong dimension is struck through and the correct one written beside it, often clouded so it is picked up as a change. Dimension errors are among the most consequential defects on a drawing because they propagate — a wrong setting-out dimension can move a wall — so reviewers tend to cloud and tag them rather than leave them as a loose strikethrough.

Hatch corrections

Hatching is the fill pattern that denotes a material — brick, concrete, insulation — or a region. A hatch correction flags that a pattern is wrong, missing, at the wrong scale, or crossing a boundary it should not. The markup is usually a cloud or arrow on the offending fill with a note naming the right material or pattern. These are easy to miss precisely because hatching reads as background, which is why a deliberate markup matters.

Highlights

A highlight is a translucent wash of colour laid over an area to draw the eye or group related items, without hiding what is underneath. Reviewers use highlights to say "this whole zone needs attention" or to colour-code by discipline or status. A highlight is softer than a cloud — it emphasises rather than asserts a specific change — so it often pairs with a text note that says what the emphasis is for.

How reviewers actually use these symbols

Symbols on their own are vocabulary; a good review is grammar. The point is not to decorate a drawing with marks but to leave a set of instructions another person can act on without having to ask what each one means. A few habits separate a useful markup from a confusing one.

• Anchor every comment. A leader from each note to its exact element removes the "which one did you mean" round trip that wastes a correction cycle.
• Say what is wrong and what is right. A crossout with no replacement deletes a problem but creates a guess. Supply the intended value.
• Cloud what changes, tag what is traceable. Use a cloud to make a change visible and a delta to make it findable; together they survive into the record.
• Match the symbol to the severity. A highlight for "look here," a cloud for "this changed," a crossout for "this is wrong" — reserving the stronger marks keeps them meaningful.
• Keep the layer separate. Markups should sit clearly above the drawing, never be mistaken for it, and be removable once resolved so the next reviewer starts clean.

A concrete example shows how the symbols combine. Suppose a checker is reviewing a ground-floor plan:

• A clouded dimension with the corridor width struck through and 1500 written beside it, tagged delta 2 — the corridor is below the accessible minimum and must change.
• An arrow from a margin note to a single door, reading "swing fouls the WC layout, reverse handing."
• A callout bubble ringed in red where the stair detail reference points to the wrong sheet number.
• A hatch correction clouding a wall shown in blockwork that should be reinforced concrete, with the right pattern named.
• A highlight over the whole plant room, with a note that the room needs a coordination review with the services engineer.

Read together, those five marks are a complete, actionable brief. The risk is what happens next: on paper, each one depends on someone remembering to act on it, and there is no record that they did.

Where Archi Check fits

Archi Check is purpose-built QC software for architectural drawing sets, and its markup tools produce exactly the symbols in this guide — cloud, arrow, callout, text, highlight, freehand, rectangle, pin, and stamp. The difference is what each mark becomes once you place it. In Archi Check a cloud or an arrow is not static ink on a PDF; it is a tracked comment that carries the reviewer's name, the date, the sheet and revision it sits on, and a status.

That status is the part paper markups never had. Every symbol moves through Check → Correct → Verify → Close: a checker raises a clouded dimension, it is assigned to whoever owns the fix, the correction is made, someone other than the author verifies it, and only then does the item close — with a record of what changed. A crossout cannot quietly vanish, because it stays open until it is verified. A callout flag cannot be lost in a stack of redlines, because it lives in the register beside the drawing. You mark up the full-size sheet on one screen using the markup tools while the register tracks every symbol on the other, in the two-screen workflow.

Because Archi Check keeps your QC data in your own project folders rather than a vendor cloud, the whole markup history — every cloud, every delta, every closed crossout — belongs to you and stays with the project. Archi Check runs on Windows today, with macOS coming soon, and there is a 14-day free trial.

FAQ

What does a revision cloud mean on a drawing?

A revision cloud is a wavy loop drawn around an area of a drawing that has changed or needs to change. Its job is to direct the reader's attention straight to the affected region rather than make them compare versions line by line. During a review it flags an area to correct; on a published drawing it records that the enclosed area changed in a given revision. The cloud method usually shows only the most recent revision's changes.

What is the difference between a revision cloud and a revision delta?

A revision cloud shows where a change is by encircling it; a revision delta — a small numbered triangle — shows which change it is by tying that area to a row in the revision table. The cloud is the location, the delta is the index. Used together, the change is both visible on the sheet and traceable in the register. Clouds are often cleared between issues, while deltas tend to accumulate as a running record.

What does a crossout or strikethrough mean on a markup?

A crossout is a line drawn through text, a dimension, or an element to mark it for deletion or replacement. On its own it means "delete this." With a correct value written alongside it means "this is wrong, use this instead," which is the usual form on dimension and text corrections. Good practice is always to supply the intended value rather than only striking out the wrong one, so the corrector is not left guessing.

What is a callout bubble used for?

A callout bubble is a circle or oval that cross-references parts of a drawing set, most often linking a plan to an enlarged detail or a section. It usually carries a detail number over a sheet number telling the reader where the related view lives. As a review markup, a callout flag points out that a reference is missing, wrong, or aimed at the wrong sheet — a common coordination defect in large sets.

Are digital markup symbols the same as red-pen redlines?

They mean the same things — a cloud, arrow, or crossout carries the same instruction whether it is in red ink or on a PDF. The difference is what happens after. A paper redline depends on someone remembering to act on it and leaves no record that they did. A digital markup in QC software can carry an owner, a date, and a status, so each symbol can be tracked from raised to verified to closed with a full audit trail.

Make every markup symbol a tracked comment

Markup symbols only help a project if the instruction behind each one is acted on and recorded. If your clouds and crossouts still live as ink on a PDF, see how Archi Check turns each symbol into a tracked QC comment with a complete audit trail: Try Archi Check free for 14 days.

Related guides

Keep building out your drawing QC process with Archi Check and these related guides:

• How to redline a drawing the right way
• Drawing approval stamps explained
• ISO 19650 status codes explained
• What is drawing QA/QC?

Archi Check is an independent product by Archi for architectural drawing QA/QC. Product names and trademarks referenced belong to their respective owners and are used for identification only.