Common CAD terms

What you'll learn

• Describe a position using an origin and coordinates.
• Distinguish dimensions, units, scale and screen zoom.
• Explain the organisational role of a layer.

Position and size

• The origin is the reference position, commonly written as (0, 0) in a 2D drawing.
• A coordinate gives a location relative to that origin. For example, (40, 20) is 40 units across and 20 units up when those are the drawing's axis directions.
• A dimension states a measured size or distance, such as a panel width or the spacing between holes.
• A unit gives those numbers meaning. A width of 100 is ambiguous until you know whether the drawing uses millimetres, inches or another unit.
• Scale is the relationship between drawing size and intended real size. A 1:2 printed view is half-size; it does not mean the underlying part should be manufactured at half-size.

Zooming in changes how large geometry looks on your screen. It does not change the geometry's stored dimensions. In most CAD workflows, model geometry is drawn at its intended real-world size; presentation or print scale can be applied separately. Before using a file, check its units and intended physical size rather than judging size by appearance.

Layers and organisation

A layer groups drawing elements so they can be organised or shown separately. For example, an outline, dimensions and notes might sit on different layers. A layer name or colour helps a person read the drawing, but it does not automatically define a manufacturing operation.

Key points

• Coordinates locate geometry; dimensions and units describe its size.
• Screen zoom is not the same as drawing scale or physical size.
• Layers organise elements but do not replace checking what the geometry means.