This photo illustrates the different fabrics obtained by knitting with Cotswold (on the left) and Shetland (on the right) - both as Double Knitting yarn.  So both yarns will have close yardage for the same weight and both will work up to the same tension swatch size for stitches and rows.  In this case both are also woollen spun - remember that worsted spun yarns work the same number of stitches but around 10% less rows in a tension swatch so you get less fabric, if more drape, for your yardage.

Now even if you look at the balls of wool you will see a considerable difference in appearance too.

Both these sheep are hill sheep although the Cotswold has a balmier climate than the Shetland in its heritage.