Chapter 4. Specifying Coordinates
Specifying points in a drawing is one of the most fundamental tasks you do in AutoCAD and AutoCAD LT. Unless you know how to specify a point, you can't draw anything real, whether a house or a gasket. Most objects you draw have a specific size, and you need to specify that information. You draw lines, arcs, and circles by specifying the coordinates of points on the screen. As with most tasks, AutoCAD and AutoCAD LT offer many ways to accomplish this.
Understanding the X,Y Coordinate System
AutoCAD and AutoCAD LT work the same way as the graphs with X and Y axes that you plotted in high school. Look at two displays of the User Coordinate System (UCS) icon, as shown in Figure 4.1. The UCS icon on the left is the default for 2D drawing; the one on the right is the default for 3D drawing and includes the Z axis. In this chapter, I focus on the X and Y axes.
The X arrow points along the X axis in the positive direction. This means that as you go in the direction of the arrow, the X coordinates increase. The Y arrow points along the Y axis in the positive direction. Using this system, every 2D point on the screen ...