Associative Dimensioning is one of the most powerful out of the box features that AutoCAD has to offer. Associative Dimensions are groups of entities that comprises of text, lines arrow heads, or other pointing styles, that form a single entity. There are two modes for Associative Dimensioning on (Associative) or off (normal), and this is controlled by the system variable dimaso. AutoCAD automatically places the Associative Dimensioning on a layer called defpoints, this layer holds the points that define the dimensions end points. You can turn an Associative Dimensioning into a normal dimension simply by exploding it, however you can not turn a normal dimension into an Associative Dimension.

Associative Dimensioning Commands LINEAR and ALIGNED.

The Linear and Aligned commands are the most basic to the Associative Dimensioning scheme, but with a good understanding of these two commands you can save yourself hours in the dimensioning of your work. From the Draw pulldown, highlight the dimensioning flyout and there you will find the Associative Dimensioning command set. Draw a simple wide flange beam then select Linear from the flyout and by getting a mid-snap select the top and bottom mid point of the beam. Frame A shows Linear dimensioning using the Vertical option. Frame B is using the Horizontal option. Frame C uses the Rotated option. The Vertical and the Horizontal options can also be obtained by dragging the cursor to the sides or top and bottom of the entity which is being dimensioned. The Rotated option may be best substituted with the Aligned command, because the Rotated option requires you to know the angle of the entities in which you are dimensioning.

Changing dimensions when an object is edited (The Association)

The true power of Associative Dimensioning is realized when a revision to a drawing comes through, or a design changes. If you used Associative Dimensioning on your base drawing, you can edit your entities and have the dimensioning change as well. One brief note; even though you used snap points to dimension your object, the dimensions are not a function of the objects' snap point. Therefore scaling or stretching your objects will not automatically scale or stretch your dimensions. In order for the dimensions to be updated when the object is edited, you will need to edit the dimension in the same manner as the object. To stretch an object you will cross the dimension lines as well as the objects that need to be edited in the same fashion as if you were just editing an objects entity(s). When you stretch all of these entities your dimensions will reflect the change immediately. To scale an object, Window or Cross the object and the dimensional information, select a GRIP, type in SC and then you can select a scale factor. After you accept the scale factor, your entity will be at the new scale and the dimensional information will reflect the new scale as well.