AutoCAD/Layout Space & Model Space

Layout Space/Model Space
Layout Space is typically used as an area for drawing entities that are not real-world objects, but rather entities that are informational in nature (annotations, border and title block, notes, etc.) and therefore can always be drawn at the same size they will be printed at. It has been long-debated about the usefulness of Layout(Paper) Space, especially since AutoCAD introduced xRefs and the ability to clip them. Many users find working solely in Model Space an efficient method of working in CAD (ala Microstation), however both methods of working in AutoCAD have their pros and cons, and what method a user may choose will largely depend on personal preference and/or the preferred method of the company one works for.

Model Space
Model space is basically "the real world". Everything is drawn at a scale of one to one (where meters, millimeters or inches are the preferred drawing units) and all drawing components are positioned at the correct distances from each other, regardless of what sheet of paper they may end up being printed on. The drawings may also be positioned on a specific coordinate system, such as a national mapping grid, in order to integrate accurately with other drawings.

Layout (Paper) Space
A typical Layout Space layout will consist of a standardized title block containing information about the drawing; drawing number, date completed etc. This title block will be drawn to accurately fit on a standardized sheet of paper. For example, a sheet of ISO A1 measures 841mm by 594mm. Thus, a title block for printing on such a sheet may measure 820 drawing units by 570. It can then be printed out at a scale of 1 to 1, and will fit on the page nicely.

Viewports
All this is of course well and good, but how do we get the actual drawing information from model space into this titleblock? To do this, we utilize an item known as a viewport. A viewport is a shape (usually a rectangle but can be any shape) that is drawn into paper space. Think of them as a TV screen. Inserting a viewport into paper spaces "places a camera" into model space. You can change the angle of view, the scale factor and many other variables in the viewport settings. These changes only effect this one viewport. This lets you have, for example, one large viewport of a building site at a scale of 1:100, and right beside it another showing a detailed area at a scale of 1:10. It's the same building site, and it exists only once in model space, but it is represented twice in two different ways in the final drawing. The obvious advantage of this is any changes made in model space will instantly update in every viewport, keeping all your printable drawings up to date.