What Is CAD and What Can You Do With It?
CAD stands for computer-aided drafting or computer-aided design: you draw technical plans on a computer instead of on paper, using precise coordinates, dimensions, and reusable parts. It is the right approach when a drawing has to be accurate, measurable, or shared with someone else — building plans, interior layouts, mechanical parts, schematics, and diagrams. If your task is a rough sketch or an illustration, general drawing software is usually simpler; if measurements and scale matter, CAD is the tool for the job.
2D vs 3D CAD
The two categories solve different problems.
- 2D CAD produces flat drawings: floor plans, elevations, section views, wiring and hydraulic schematics, part outlines. You work in a plane with lines, arcs, circles, and text, and you control scale for printing.
- 3D CAD builds a model in space, from which you can generate views, check fits, or drive manufacturing. It is more powerful and has a steeper learning curve.
Many drafting tasks never need 3D. Plans, layouts, and diagrams are naturally 2D, which is why 2D tools remain the fastest route for them.
What you can produce
Typical outputs of a 2D CAD workflow include:
- Architectural plans and building drawings
- Interior layouts and furniture arrangements
- Mechanical parts and assemblies drawn as views
- Schematics and diagrams (electrical, hydraulic, process)
- Dimensioned drawings for fabrication or permits
- Scaled printouts, including drawings split across multiple pages
Core concepts worth learning first
These ideas appear in every 2D CAD system, so learning them once transfers between tools.
| Concept | What it does |
|---|---|
| Layers | Group drawing content so you can show, hide, or print categories separately (walls, dimensions, notes) |
| Blocks | Group objects into a single reusable unit, so a repeated symbol is edited once and updated everywhere |
| Units | Set metric or imperial measurement so coordinates and dimensions mean something real |
| Object snaps | Lock the cursor to exact points — endpoints, midpoints, intersections — instead of eyeballing |
| Dimensioning | Add measured annotations that update with the geometry |
| Construction and modification tools | Draw lines, arcs, circles, ellipses, splines, polylines; then move, copy, rotate, trim, offset |
File formats: DXF and DWG
DXF and DWG are the standard exchange formats for CAD drawings. DXF is widely readable across applications; DWG is the native format of AutoCAD and common in professional workflows. If you need to send a drawing to a contractor, client, or machine shop, being able to read and write these formats matters more than which program you drew in. Check format support before committing to a tool.
Where free and open-source 2D CAD fits
QCAD is a free, open-source 2D CAD system for Windows, macOS, and Linux, released under GPLv3, with the current version listed as 3.33. Its stated design goals are modularity, extensibility, and portability, and it advertises an intuitive interface that does not require prior CAD experience. Its feature set covers the concepts above: layers, blocks, metric and imperial units, DXF and DWG input and output, printing to scale and across multiple pages, over 40 construction tools, over 20 modification tools, object snaps, measuring tools, and a part library of more than 4800 CAD parts. It also includes a scripting interface and command-line conversion tools.
That makes it a reasonable starting point if you want to learn 2D drafting without a licence commitment, or if you need a cross-platform tool for plans and diagrams. The trade-off to weigh: a free 2D tool covers flat drafting well, but it is not a substitute for 3D modelling or for the collaboration features of a commercial suite.
A simple starting path
- Pick a 2D tool that reads and writes the formats you need to exchange (DXF and DWG are the safe defaults).
- Set your units — metric or imperial — before drawing anything. Changing units later distorts dimensions.
- Set up layers for the categories in your drawing, so you can control visibility and printing.
- Draw with construction tools, using object snaps so endpoints and intersections are exact.
- Annotate with dimensions rather than typing measurements as text, so the drawing stays consistent if geometry moves.
- Reuse blocks for repeated symbols instead of redrawing them.
- Print to scale and verify the result — including multi-page output if the drawing is larger than your paper.
If you get stuck, the usual culprits are wrong units, snaps turned off (so lines do not actually meet), and drawing on the wrong layer.