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All the action takes place in the Drawing View Window. As mentioned earlier, the Drawing View Window might display Model Space or Paper Space. To determine which space you are in look for the icon in the lower left corner of the screen. 
If there is an icon resembling the one to the right, with two arrows marked "X" and "Y", you are in Model Space. At the bottom of the Drawing View Window, just above the command line, there are tabs like the tabs for file folders. One says "Model". Clicking on this tab places you in the main Model Space drawing window. The default background color for this space is black.
The other tabs are Layout tabs. When you click on a Layout tab, you will open the designated Layout in either Paper Space or a Model Space Viewport. The default background for a Layout is white. You make as many Layouts as you like and call them whatever you like. A Layout is a Paper Space drawing with Viewports into Model Space. Layouts are an easy way to set up a drawing for printing or plotting.
If Paper Space is active, the UCS icon changes to a right triangle. Click on one of the Layout tabs at the bottom of the screen, and click the MODEL toggle if necessary, to activate Paper Space. You cannot draw three-dimensional objects in Paper Space. Paper Space is ideal for title blocks and boders. Using the MVIEW command you create a "Multiple Viewport" that open a view into Model Space. You can make several. Clicking on the PAPER toggle in the Active Status Bar will take you into the last active Viewport. Notice that the icon changes from the right triangle to the double arrow icon. The Model Space icon appears in the corner of all Viewports with the border of the active Viewport appearing much bolder. You can now draw, zoom, and pan in the Model Space Viewport. When you return to Paper Space, the current view will be remembered.
For now, lets stick with the main Model Space window. Click on the Model tab to get back there. We will ignor Layouts until it is time to print.
The ZOOM command is the key to the drawing area. If you don't have a drawing open, open one (File/Open). AutoCAD should have some in the "Sample" directory. Type[Z] and push enter the Zoom command dialog appears: "Specify corner of window, enter a scale factor (nX or nXP), or [All/ Center/ Dynamic/ Extents/ Previous/ Scale/ Window] <real time>:". Pick two points on in the drawing area. You should have "Zoomed" in so that only that area is visible in the drawing screen. Enter [Z] again and press [E] at the zoom dialog. Press enter. The drawing zooms to the "Extents" of the drawing, in other words, everything that is turned on in the current drawing space should be showing. Zoom All is similar. Zoom All zooms to the Extents or to the "Limits" of the drawing (I'll explain), whichever is greater.
Zoom Window is similar to the first "real time" zoom. Pick a point on the drawing screen and drag a window. Pick another point and the view window zooms or resizes to those coordiantes. Zoom Center allows you to pick a location for the center of the zoom window and specify a height in drawing units. Zoom Dynamic temporarily zooms the drawing to the extents in memory, which may be less than the full extents of the drawing, and places a box around the crosshairs. Move the box around and pick a spot (left mouse click), pull the box larger or smaller. Pick again. Continue until you have the spot you want, then right mouse click. The drawing view zooms to the box. Zoom Previous zooms to the last drawing view.
Zoom Scale zooms the drawing view scale by a factor (nX or nXP). Enter [Z] and press [S] at the zoom dialog. Press enter. Enter [5x] at the command prompt and press enter. The drawing view scales up five times larger. Zoom Scale [nXP] is for zooming a viewport, covered later, to a factor of the Paper Space units. This is very useful for scaling windows for plotting.
Not had enough yet? There is an additional way to zoom. Right mouse click. On the Shortcut Menu that appears click Zoom. The crosshairs become a magnifying glass with plus and minus symbols. Left mouse click and drag the cursor up the screen to move closer to the view, and drag down the screen to move away from the view.
A zoom command can be performed in the middle of another command. This is a Transparent zoom invoked by placing a single quote (') in front of the ['Z]. This is useful if you are drawing a line from one spot but the next spot to pick is not in the drawing view window. A transparent Dynamic Zoom, ['z] [d], will allow you to move to another portion of the drawing. There are other transparent commands such as Pan, ['P].
PAN is also found on the Shortcut Menu. Type [P] and the crosshairs appear as a hand. Left mouse click and drag the cursor in the direction that you want to slide the view window. To get out of the Pan mode, right mouse click and select Exit or press the Escape key.
LIMITS, I told you I[d get back to them, allow you to set drawing boundaries. Type [limits] and press enter. The command line prompts read, "Reset Model space limits: Specify lower left corner or [ON/OFF] <0.0000,0.0000>:" If you set limits to [0,0] by [50'-0",25'-0"] and turn limits [ON], you will be disallowed from drawing outside of that box. Zoom All will zoom to those limits even if nothing is drawn yet. Additionally the grid command will only fill the box defined by the limits.
And there is another way to get around: Aerial View can be picked off of the View pull-down menu. A tiny view of the entire drawing appears in a seperate window that hovers in the corner of the drawing. Click inside the Aerial View Window to activate a view box and move the curser in the window. The drawing view in the main Drawing View Window follows the view box in the Aerial View Window. Click and drag right or left in the Aerial View Window to cause the view in the Drawing View Window to zoom in or out. Aerial View is very useful for getting about in large drawings.
Cartesian coordinates are those numbers learned in algebra class to make graphs. An (X,Y) pair of numbers locates a point somewhere in two dimensional space relative to an initial Origin or (0,0) point and an orientation direction. An (X,Y,Z) will define locations in three dimensional space. When you begin a drawing AutoCAD starts with a predefined (0,0,0) point and an initial grid orientation, which it calls the World Cooridinate System. The UCS (User Coordiante System) icon in the lower left corner of the screen (or at the Origin point, depending on user settings) looks like the arrows on the right in Model Space. These arrows point in the X and Y directions. The "W" just below the Y indicates that the World Coordinate System is now active, as opposed to another user defined system. and the boxed in corner indicates that you are looking at the drawing plane from above.
The UCSICON command allows you to turn the icon OFF or ON, and to have it appear at the ORigin point (if it is on the screen) or in the bottom left corner (Noorigin). When you work in three-dimensions, the UCS settings change frequently so the UCS icon becomes very important.
The drawing units for (X,Y,Z) locations and for angles are determined by the UNITS command. The Units command brings up the dialog box on the right, (in release 14 or earlier a command line dialog). If you wish to work in English "Imperial" units (feet and inches), Architectural or Engineering units will work best. Architectural units display partial inches as a fraction, whereas Engineering units express them as a decimal. Two feet one and a half inches is 2'-1-1/2" in Architectural Units and 2'-1.50" in Engineering Units. For metric drawing use Decimal units. You won't likely need Fractional or Scientific units.
Units controls the display of units and how AutoCAD interprets numbers typed at the command line when units are called for. It does not control the dimension units. Even though the units are set to Architectural, AutoCAD recognizes decimal units as easily as fractions. AutoCAD interprets [18.125] as 1'-6-1/8".
Angles are most easily set in Decimal Degrees, but for those who have a exotic needs they can be set in degrees/minutes/seconds, grads, radians, or surveyor (cardinal direction) units. By default, AutoCAD sets 0° at the 3 o'clock position and adds positive increments in a counter-clockwise rotation. Thus, 12 o'clock is 90°, 9 o'clock is 180°, and 6 o'clock is 270°. A full 360° returns to 0°. However, the units command allows the user to start 0° at any point around the dail with the "Direction", submenu, and to cause degrees to be counted off in a clockwise direction with the "Clockwise" checkbox.
Precision sets the display precision of Length and Angle units, not the Dimension precision. Set this high enough to accurately place units, without becoming cumbersome. "Drawing units for DesignCenter blocks" is supposed to tell AutoCAD how to interpret blocks inserted through the design center, but the command still needs work.
When a drawing command is activated, you will be asked to pick a point, select an object or point, or locate an element. This can be as simple as choosing a spot on the screen with the pick box and clicking, or it may be an elaborate dialog of tracking, snaps, submenu choices, zooming, panning, etc. before the actual point or object is chosen and picked.
Precision is important. Later, when you dimension a drawing, edit using trim or extend, create polylines from lines or hatch them, sloppiness will bite you back. You can waste a lot of time trying to track down a tiny opening between lines. AutoCAD's Snap, Object Snaps, Ortho Mode and other tools making drawing with precision very easy.
Neatness counts. AutoCAD performs better with precise linework.
CADvise:
A point can also be entered at the command prompt as a set of two (X,Y) or three (X,Y,Z) coordinates. If you place an element above or below the drawing plane using a positive or negative "Z" coordinate it will not react to elements in the drawing plane in the same way. Until there is a good reason, type in two coordinate points, AutoCAD will add the current elevation, which should be "0", as the third or "Z" coordinate.
A point can also be added Relative to the last chosen point. By typing [@X,Y] the new point will be located at a distance of X along the X axis from the last point and Y along the Y axis from the last point or (X¹+X²,Y¹+Y²). This also works for [@X,Y,Z] entries. Points can also be entered as Polar coordinates relative to the last chosen point. Typing [@X<W] enters a point X distance in the W direction from the last chosen point.
The above discussion assumes a Verb-Noun working method, whereby an action is asked for by activating a command (the Verb), and then drawing objects are selected (the Noun). By now you[ve probably figured out that there are a lot of ways to do things in AutoCAD. Yes you can reverse the process in many cases. With the "Noun/verb selection" option checked under the Selection tab in the Options menu, you can select objects and then type a command to perform on them.
If no command is active, picking in the Drawing View Window Selects drawing objects. The selected objects turn into dashed lines, (called a marquee in some drawing programs), and display grips (little boxes at the end points). If you select a menu command or enter a command at the prompt, AutoCAD will attempt to perform the command action on the Selection set.
If you are selecting objects for an active command and you select the wrong object, type [U] for undo and press enter or right mouse click. The selection will be unselected but all other selections will remain. Another way to unselect is to push shift while selecting a previously selected object. The object is removed from the selection set.
While we are on selection sets, a common problem is objects that are very close to each other or directly on top of each other so that selecting the proper element is impossible. In this case, press Control while picking the object. If the wrong object is selected, pick again. The selection cycles through the possibilities within the pick box.
When in doubt press [F1]. The Help dialog has the user manual, a searchable index, and a "find" function that searches the entire help file. Included are links to other help files, such a LISP programming help or Visual Basic help. From the Help pull-down menu, select
If you get into big trouble, don't panic. Call your AutoCAD dealer. The dealer often has an answer so fast that you[ll feel foolish. Don't worry, even the dealers don't know it all. AutoCAD is very big and very complex. That's why it is such a powerful tool.
Refer back to Chapter 3 for ways to keep up training and network with other users.
If you make a mistake and, say, erase something important, don't panic. There is an UNDO command. You can undo many commands at once by repeating the [U] command several times or by typing [Undo] and entering a number to indicate the number of commands to Undo. If you undo too many, [Redo] restores the last undone command.
Now it's time to learn to draw. We'll start the next chapter with simple AutoCAD two-dimensional drawing objects or "Primitives".
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