A vector is a line with magnitude and direction. In CAD-speak, it is a line defined by its end-points and nodes, as opposed to a line formed from a series of points on a bitmap.
AutoCAD is the 'industry standard' Computer Aided Design software. It is a relatively expensive CAD programme and there are cheaper alternatives which garden designers can use. CAD has undoubted advantages, summarised in the phrase 'faster, cheaper, better' but there is a worry about the CAD design technique influencing the design product.
AutoCad is reputed to have begun as a draftsman's programme in the days when senior partners, thinking of keyboards as being for secretaries and other exploited menials, employed CAD technicians to operate the machines. But the programme is developing. It can be linked to databases, can have a GIS bolt-on, and is being adapted for internet-connectivity. These facilities all provide opportunities to move way beyond computer-aided-drafting. The most interesting prospect it of drawing information from the world wide web and interpreting it with specialist software to assist in clarifying the multifarious interpretations of the nature of the world - upon which the art of landscape design resides.
A vector line, defined by co-ordinates and nodes.
A bitmap line - drawn as a series of points in a raster.