A second division classifies embroidery according to whether the design is stitched on top of or through the foundation fabric: In Surface embroidery, patterns are worked on top of the foundation fabric using decorative stitches and laid threads. Surface embroidery encompasses most free embroidery as well as some forms of counted-thread embroidery (such as cross-stitch). Canvas work threads are stitched through a fabric mesh to create a dense pattern that completely covers the foundation fabric. Not all canvas work is counted-thread embroidery. There are printed and hand painted canvases where the painted or printed image is meant to serve as a color guide. Stitches are sometimes of the stitcher's choosing. An important distinction between canvas work and surface embroidery is that surface work requires the use of an embroidery hoop or frame to stretch the material and ensure even stitching tension that prevents pattern distortion. Canvas work tends to follow very symmetrical counted stitching patterns with designs developing from repetition of one or only a few similar stitches in a variety of thread hues. Most forms of surface embroidery, by contrast, are distinguished by a wide range of different stitching patterns used in a single piece of work.