How CAD represents geometry

What you'll learn

• Tell a raster image from vector geometry.
• Identify points, lines, curves and paths.
• Explain why an open path differs from a closed profile.

Picture versus geometry

A raster image, such as a photo or scan, is a grid of coloured pixels. It can show a part clearly, but the pixels do not automatically tell CAD where its exact edges and dimensions are.

A vector drawing stores geometry as editable elements. A line can have endpoints; a circle can have a centre and radius. You can move or measure those elements without relying only on how large they appear on screen. A picture of a circular hole and a vector circle may look alike, but only the latter directly describes the circle as geometry.

The building blocks

• A point marks a location. A node is a point used to define or control part of a vector outline.
• A line is a straight segment between two points. A curve changes direction smoothly between its defining points.
• A path is a sequence of connected lines or curves. An open path has separate start and end points; a closed path joins back to its start.
• A shape or profile is an outline used to describe a feature or boundary. When it represents an enclosed area, its path normally needs to be closed.

Imagine tracing a rectangular panel. Four connected edges can form a closed outer profile. If the last edge stops just short of the first, it may still look closed at a small zoom level, but the stored path is open.

Key points

• Pixels show an image; vectors describe editable geometry.
• A tiny gap can make a visually closed outline an open path in the file.