Illustrator - Vocabulary — David Barbarash

Why this matters

AutoCAD draws objects defined by real-world coordinates. Illustrator draws objects defined by anchor points, handles, and paths — a completely different geometric model. Both programs draw with vector processes, but the two applications share almost no terminology and almost no interface logic. Understanding what Illustrator's terms actually describe is the prerequisite for using it purposefully rather than clicking until something looks right.

Core concepts

Term	What it is
Artboard	The defined output area within an Illustrator document — equivalent to a sheet of paper. A single AI file can contain multiple artboards, each representing a separate diagram or output page. Artboard size defines what exports, not what you can draw.
Path	The fundamental object in Illustrator. A path is a sequence of anchor points connected by line or curve segments. Every shape, line, and diagram element is a path or a collection of paths.
Anchor point	A node on a path that defines its geometry. Corner points create sharp turns; smooth points have direction handles that control the curvature of adjacent segments.
Direction handles	The control arms extending from a smooth anchor point. Dragging them adjusts the curve of the adjacent path segments. The longer the handle, the more influence it has on the curve.
Open path	A path with two distinct endpoints — a line or curve that doesn't close. Open paths can have a stroke but cannot be filled in a predictable way.
Closed path	A path whose last anchor point connects back to its first. Closed paths can be filled with color, gradient, or pattern. All diagram area fills require closed paths.
Stroke	The visible border or line along a path. Controlled by color, weight (in points), dash pattern, cap type, and join type. A path can have a stroke without a fill, a fill without a stroke, or both.
Fill	The color, gradient, or pattern applied to the interior of a closed path. A path can have a fill without a stroke.
Compound path	Multiple paths combined into a single object, where overlapping areas create transparent "holes." Used for objects with interior voids — doughnut shapes, text-cutout masks, complex diagram regions.
Group	Multiple objects collected into a single selectable unit. Groups can be nested. Double-clicking enters isolation mode to edit objects inside the group.
Isolation mode	Entering a group or layer by double-clicking. Objects outside the isolated context are dimmed and unselectable. Press Escape to exit.
Layer	A named organizational container in the Layers panel. Controls stacking order, visibility, and locking for objects assigned to it. Illustrator layers work like CAD layers in their organizational role but behave differently — they stack visually, front to back.
Appearance panel	Shows and controls all visual attributes of a selected object: fill(s), stroke(s), effects, and opacity. Multiple fills and strokes can be stacked on one path through this panel.
Pathfinder	A panel of boolean shape operations that combine, subtract, intersect, or divide overlapping paths into new shapes. One of the most-used tools for diagram construction.
Live Paint	A mode that allows painting enclosed regions formed by the intersection of multiple overlapping paths — regardless of whether those regions are explicitly defined as closed shapes. Useful but requires careful workflow management.
Clipping mask	A shape that defines the visible area of the objects beneath it. Everything outside the mask shape becomes invisible. Used to crop diagram content to a site boundary.
Artboard export	Exporting individual artboards as separate PDFs or image files. This is how multiple diagrams in one AI file become individual deliverable files.
Document color mode	RGB for screen display; CMYK for print. Diagrams shared digitally should be RGB. If color fidelity for print matters, use CMYK. Set this at document creation — changing modes later shifts colors.

From the office

The most consequential difference between Illustrator and AutoCAD for professional work: Illustrator has no real-world coordinate system. There is no equivalent to AutoCAD's architectural units, no drawing to scale in the traditional sense. Scale in Illustrator is a matter of importing content at a known size and maintaining proportional relationships. This is why importing your CAD plan at the correct scale is critical — everything that follows depends on it.