HOW TO MAKE A TESSELLATION:
Line Method Example 2
10. Often, for the sake of a picture, once you have shown the shape will tessellate, it may be good art to leave some of your repeating shapes out like Dr. David did, in the picture on this page. Put in something else to fill that space, like a sea and maybe a few fishsticks for the hungry sea lions.
You can see a larger version of this picture in the 'Art We Did: Dr. David's Art' section of Tessellations.org. Other 'incomplete' examples are also included there such as 'dogfight' and 'sea battle'.