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Drawing Lines

The number one command in AutoCAD is the Line command. Lines in
AutoCAD are extremely precise drawing elements. This means you can
create very accurate drawings. Lines, or any drawn object, can be as
precise as eight decimal places (i.e., 24.999999999) or 1/256.
AutoCAD is a vector based program. That means each drawn object is
stored in a numerical database. For example, a line is stored in the
drawing’s database as the X, Y, Z coordinates for its starting point and
the X,Y,Z, coordinates for its endpoint. These coordinates are all
relative to the drawings 0, 0, 0 position; called the Origin.
When a line needs to be displayed on the screen, AutoCAD reads the
line’s coordinates from the drawing database and displays a line between those two points on the screen. This means that the line will be very accurate at any scale or zoom magnification.
A raster based program, in contrast to vector based, is comprised of dots that infill a grid. The grid can vary in density, and is typically referred to as resolution (e.g., 600x800, 1600x1200, etc.). This file type is used by graphics programs that typically deal with photographs; such as Adobe Photoshop. There are two reasons this type of file is not appropriate for CAD programs:
1. A raster based line is composed of many dots on a grid (which also represents the line’s width). When you zoom in (or magnify) the line, it becomes pixilated and you actually start to see each dot in the grid. In a vector file you can “infinitely” zoom in on a line and it will never become pixilated because the program
recalculates the line each time you zoom in.
2. A CAD program, such as AutoCAD, only needs to store the starting point and end point coordinates for each line; the dots needed to draw the line are calculated on the fly for the current screen resolution. Whereas a raster file has to store each dot that represents the full length and width of the line. This can
vary from a few hundred dots to several thousand dots, depending on the resolution, for the same line.

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