One of the most basic concepts to understand in Illustrator is strokes, or the lines around objects. Objects may have a fill and no stroke, a stroke and no fill, a fill and a stroke, or no stroke and no fill. But beyond just the basic stroke, let’s take a look at the strokes palette to understand all the capabilities.
WEIGHT: Refers to the thickness of the line. By default this is measured in points, but you may enter in other units of measurement, like if you need your stroke to be exactly 0.75 inches thick, you can do that!
CAP: Controls the ends of a stroke with open endpoints. The default is butt, but I choose round occasionally, including when I need to do a dotted line. I rarely use projecting cap.
CORNER: Controls the corners of your strokes. The default is miter, and the limit controls when the stroke corner switches to bevel instead of corner. Sometimes you get spikes when your stroke corner is too sharp. To fix this, you need to either decrease the miter limit or make your corner not as sharp.
I use bevel when a stroke corner may otherwise protrude beyond the artwork I am creating. An example is in the above image. If my stroke weren’t set to bevel, then I’d have a couple of spikes protruding out the bottom of my floral motif.
ALIGN STROKE: Works only on closed paths. By default, the stroke straddles the path. This will align your stroke to the inside or outside of your path.
DASHED LINE: Check to create a dashed line.
DASH ALIGNMENT: Only available in CS5 and above, and one of the major reasons I recommend upgrading from previous versions. In previous versions, dashes and gaps are distributed mathematically, which means that the dashes and gaps may not work with the size of object you have created. The new distribution option will allow Illustrator to distribute gaps and dashes around your object without rigidly adhering to the exact mathematics.
DASH/GAP: Controls the dash and gap lengths. If you set a dash length, then the gap length, if not set, will automatically match the dash length. I usually only set one dash length and one gap length, but different gaps and dashes may be set.
For a dotted line, the dash must be set to 0pt, the cap to round, and the gap to a value larger than the weight.
ARROWHEADS: Another new addition as of CS5. Adds an arrowhead option to the beginning and/or end of your line. There are several very good options available. (Swap with the button beside the arrowhead options.)
SCALE: Controls the scale of the arrowheads. Click the lock to keep them the same scale.
ALIGN: Controls the alignment of the arrowheads.
PROFILE: Again, new as of CS5. Previous to CS5, all strokes were of a uniform weight. In CS5 and higher, you may vary your stroke width. You may either do this with these preset profiles, or you may use the Stroke Width Tool to vary the width (press shift W to find it in your tool bar). If you create a varying stroke width that you would like to apply to multiple objects, you can save your stroke width to this section.