Aligning is similar to snapping; the main difference is that for something to snap, you set up a snap target and use your mouse to move the selection close enough to that target, whereas aligning commands themselves move the selected objects by any distances necessary to arrange them in a certain way.
Alignment commands are collected in the powerful Align and Distribute dialog. Open it by pressing 
or by selecting a command in the Object menu. The basic routine is: You select the objects you want to align, call up this dialog, and click one of the buttons to perform the alignment.
Figure 7-13 shows the Align part of the dialog with all buttons annotated.
To make sense of this plethora of buttons, observe the following:
Buttons in the top line align things by moving horizontally; those in the bottom line, by moving vertically.
All the alignment buttons move objects relative to the anchor box. What exactly is considered the anchor box is changeable by the Relative to: list. The default, which works in most cases, is Selection, which refers to the united bounding box of all selected objects. However, you can instead select the bounding box of one of the selected objects (the one which was the first or the last to be selected, or the biggest or smallest one) as well as the entire page or entire drawing’s bounding box.
For example, if you have a collection of small objects and you want to align them against the top of a large background object, select everything and choose Biggest object in the Relative to: list.
Of the 10 buttons on the left, the middle ones in both rows align centers of selected objects at the center of the anchor box horizontally and vertically. The two buttons immediately to the left and the two to the right of the centering buttons press objects against the edges of the anchor box on the inside. Together, these six buttons are perhaps the most commonly used in the entire dialog. The four remaining buttons also align the objects at the edges of the anchor box but on the outside.
The two buttons on the right—those with letters on them—only apply to text objects. Every text object has a baseline origin point, and these buttons align the selected text object by these points. This is sometimes necessary because if you align text objects as regular objects by their bounding boxes, the characters with and without descenders (such as the bottom stroke of y) and ascenders (such as the stem of d) will not keep the line:
