A coordinate system consists of numbered scales that identify an initial, or base,point and the direction for measuring subsequent points on a graph. As illustrated in Figure 2.8, each pair of axes (xy, xz, yz) forms a flat plane. Most of your time working with AutoCAD will be spent drawing in the xy-plane.
F igu re 2 . 8 : The x-, y-, and z-axes and the related xy-, xz-, and yz-planes
values on one side of the origin are positive, all values on the other side are
negative, and values that fall in line with the origin have a value of 0 (zero). The
divisions along the scales may be any size, but each division must be equal.
The axes divide the coordinate system into four regions called quadrants.
Quadrant I is the region above the x-axis and to the right of the y-axis. Quadrant II is the region above the x-axis and to the left of the y-axis. Quadrant III is the region below the x-axis and to the left of the y-axis. Quadrant IV is the region below the x-axis and to the right of the y-axis. Most of your work in AutoCAD will be done in Quadrant I, and this is the area shown when you first open a drawing.
You may specify any point on this graph by giving its coordinates relative to
the origin, indicated as a combination of the X value and the Y value delineated with a comma. For example, a coordinate of 5,7 means a point on the coordinate system that is 5 units in the positive X direction and 7 units in the positive Y direction. Figure 2.9 shows a typical Cartesian coordinate system and the default region used as the drawing area in a new AutoCAD file.
You can also start the ERASE command by typing E↵. In this next exercise,
you’ll use the LINE command again, but instead of picking points in the drawing
area with the mouse as you did before, this time you’ll enter the x- and y-coordinates
for each point from the keyboard. To do this, follow these steps:
1. Click the Erase icon in the Home tab ➢ Modify Ribbon panel.
2. Type ALL↵. The objects in the drawing become dashed to indicate
that they are selected.
3. Press ↵ to clear the screen.
4. Click the Grid Display icon on the status bar to display the grid if it is
not already turned on (blue glow). The gridlines that display provide a
graphical representation of the Cartesian coordinate system used by
Now begin drawing lines again by following these steps:
5. Start the LINE command by clicking the Line icon in the Home tab ➢
Draw panel on the Ribbon.
6. Type #7,2↵ to start the first line segment at a location 7 units above
and 2 units to the right of the drawing’s origin point.
7. Type #11,3↵ to determine the endpoint of the line. Then enter the
8. Press ↵ again to end the command.
Figure 2.10 shows the completed drawing with coordinates and
direction arrows added for clarity.F igu re 2 . 1 0 : Completed drawing showing coordinates and direction of lines
The lines are similar to those you drew previously, but this time you know
where each point is located relative to the 0,0 point. In the drawing area, every
point has an absolute x- and y-coordinate. In steps 5 through 7, you entered the
x- and y-coordinates for each point. For a new drawing such as this one, the origin
(0,0 coordinate) is in the lower-left corner of the drawing area, and all points
in the drawing area have positive x- and y-coordinates.
Let’s explore how the cursor is related to the coordinates in the drawing:
1. Click the Zoom Extents icon located on the Navigation bar (the semitransparent
vertical bar under the ViewCube®), or type ZOOM↵E↵ to
adjust your view to show the extents of the drawing area.
2. Add the Coordinates readout to the status bar by clicking the
Customize button on the status bar, and then selecting the
Coordinates option from the resulting menu shown in Figure 2.11.
F igu re 2 . 1 1 : Adding the Coordinates readout to the status bar3. Move the cursor around, and notice the left end of the status bar at
the bottom of the screen. This is the coordinate readout, and it displays
the coordinates of the cursor’s position, as shown in Figure 2.12.
F igu re 2 . 1 2 : The x- and y-coordinates of the cursor are shown at the bottom
of the AutoCAD window.
4. Move the cursor as close to the lower-left corner of the drawing area
as you can without it changing into an arrow. The coordinate readout
should be close to 0.0000, 0.0000, 0.0000.
5. Move the cursor to the top-left corner of the drawing area. The readout
changes to something close to 0.0000, 7.0000, 0.0000, indicating
that the top of the screen is 7 units from the bottom.
6. Move the cursor one more time to the upper-right corner of the
drawing area. The readout still has a y-coordinate of approximately
7.0000. The x-coordinate now has a value around 10.5.
The drawing area of a new drawing is preset with the lower-left corner of the
drawing at the coordinates 0,0.