Geometry & coordinates

Every IDML page item is placed and shaped by one shared coordinate space — points, a top-left origin, and a per-item transform.

In short: Before a frame can hold text or a shape can be filled, it has to be somewhere. This section is about that somewhere: the coordinate space an IDML document draws into, and the handful of attributes that place and shape every page item. Distances are measured in points, the origin sits at the page's top-left with Y growing downward, and each item carries its outline in its own inner space that an ItemTransform slides onto the page. Learn that space once here and every later element page — TextFrame, Rectangle, Oval — gets shorter, because they all read the same geometry the same way.

We put this section ahead of the chapters on visible elements deliberately. A TextFrame, a Rectangle, an Oval — they all carry the same geometry attributes, read the same way by the parser. Learn the space once here and every later element page gets shorter.

What you need to know

The space itself is simple, and three facts cover most of it:

• Units are points. Everything numeric — bounds, transforms, path coordinates — is in points, 72 to the inch. See units & origin.
• The origin is the page's top-left, and Y grows downward. This is flipped from the math-class convention; it trips up everyone once.
• Each page item has its own inner coordinate space. Its shape is authored around its own origin, and an ItemTransform slides (or rotates, or scales) that whole space into the page.

On top of that sit two ways IDML records where a shape is and what it looks like:

• GeometricBounds — the axis-aligned bounding rectangle, in an axis order that surprises people: y1 x1 y2 x2.
• PathGeometry — the actual outline, as one or more contours of anchor points. This is how real InDesign exports describe every shape, even a plain rectangle.

Where it gets interesting

Two path constructs earn their own pages because they are easy to get subtly wrong:

• Compound paths — more than one contour in a single shape, which is how a hole gets punched.
• Open paths — contours that are not closed, flagged by PathOpen and covered alongside the path anatomy on the PathGeometry page.

Each page is grounded in what our parser actually does with the attribute, and carries a live example you can edit and re-render.

Frequently asked questions

What coordinate system does IDML use? IDML geometry uses points (1/72 inch) as its only unit, with the origin at the page's top-left corner and Y growing downward — so a larger Y is further down the page. It is the same orientation throughout the format; only the origin shifts between a page's space and an item's own inner space.

Why does the page space matter before the element pages? Every visible page item — TextFrame, Rectangle, Oval, GraphicLine, Polygon — carries the same geometry attributes and the parser reads them the same way. Understanding the units, origin, bounds, and transforms once means the later element pages don't have to re-explain placement at all.

How is a shape's position recorded separately from its outline? A shape's outline (its PathGeometry or its GeometricBounds) is authored in the item's own inner coordinate space, usually around its own origin. Its ItemTransform — a six-number affine matrix — then maps that whole inner space onto the page, so where a shape is and what it looks like are stored independently.