When making a conversion like this the first thing that you have to do is carefully review the pattern. The main things to look for are stitches that cross the end of round marker (also denoted in patterns by "dancing markers") and asymmetries in the pattern that might not lend themselves to being split into a cape (or semi-circular) shawl. This kind of pattern review is most easily done by looking at the charts, so for the non-chart knitters I strongly recommend that you take the plunge and learn how to read charts. It really isn't that hard. I recommend J. C. Briar's book Charts Made Simple: understanding knitting charts visually. You can still spot these things by looking at the written directions, provided that they are well written - just look for the pattern repeats and then look at what other stitches you have to do that are not included in the pattern repeats.
For Chart 1 of Evenstar we are very fortunate in that the motif is symmetrical, although it does wrap across the end of round marker on rows 7, 13 and 27. Row 7 begins with a special stitch - increase 7 in a k3tog. The other two rows begin with a slip 1, k2tog, pass slipped stitch over (s1k2togpsso). That special stitch is going to take a little careful thought (and some experimentation), so lets look at the easy stitch first. The s1k2togpsso stitch is a type of double decrease, we're taking 3 stitches and turning them into one. If you split that stitch apart by converting from knitting in the round to knitting flat and you still want to retain symmetry in the design you would need to start those rows with a k2tog, yo and end those rows with a yo, ssk. That takes care of the double decrease, but we need 4 stitches, not two. What to do? Easy, add an extra stitch at the end of the row. When you're not knitting one of those 3 rows you just knit or purl that stitch as appropriate.
Now lets go back and look at the special stitch. This one is easier to decipher if you look at the chart. You will note that in row 6 there are 3 "no stitch" spots, so you know you need to increase 3 stitches. After a little trial and error (and you have to be willing to experiment) I decided that an increase 4 in a k2tog is the way to treat this special stitch at the beginning and end of the row. A word about the increase stitch. Susan Pandorf offers 3 different ways to work this stitch and recommends that knitters try out each of the methods while working the swatch to determine which one they like best. I prefer the method that uses the yarn overs. It results in a nicely symmetrical Evenstar, with an open center, and is also easy to work. There is just one small problem with using yarn overs, you have to do an odd number of increases because the yarn over has to be worked between two regular knit stitches and at the beginning and end of the row we need to work 4 increases. To handle that I did the knit, yo, knit, and ended with a knit into the back of the stitch.
Now that we have all of those things worked out (and hopefully you've annotated your pattern appropriately) take a look at the pattern again and ask yourself if there are any other modifications that you would like to make. For example, in rows 11 and 25 there are k4tog stitches. I decided to work the first k4tog in row 11 as a ssssk and the second k4tog in row 25 as a ssssk, so that they would both slant away from the central petal. The other thing to consider before you begin is whether you want to add beads, and where you would like to add them. I decided to add beads to the points of the Evenstar.
Okay, we're now ready to figure out how many stitches to cast on. Looking at the pattern we note that this is a traditional "Pi" shawl so it starts out with a number of rounds of knitting followed by increase rounds. The last increase round before Chart 1 gets us to the stitch count for that round, which is 144 stitches. But wait, we need an extra stitch to work this flat, so we need 145 stitches when we complete that increase round. Obviously we don't want to start the shawl with 145 stitches, so go back to the stitch count before the increase round, which is 72 stitches. We also have to consider edge stitches. I like to work a 3 stitch garter stitch border, which would bring the cast on stitch count up to 78. I cast on 78 stitches and knit 4 rows and then worked the increase row. When you work one of these yo, k1 increase rows in a circular shawl you double the number of stitches, but when you work one of these yo, k1 increase rows while knitting flat you wind up at the end of the row and you've just knit a stitch and there are 3 edge stitches left. If you do one more yarn over before you knit those 3 edge stitches you will actually increase by 73 stitches instead of 72, which gets us that extra stitch that we wanted for Chart 1. Pretty cool, huh.
Pattern: Evenstar Shawl by Susan Pandorf, converted into a cape
Yarn: The Unique Sheep Eos in Midnight Delight
Needle: US 3 (3.25 mm)