Technically, those who coined the phrase 'zentangle' define it as filling a 3.5" square with patterns they call tangles. Anything that doesn't fit into that description but still uses the tangles has been coined 'zentangle inspired art'.
I jumped right in to one of those. In exploring what zentangles are, I found the zentangle gallery on flickr. While on there, someone had done one ZIA that really resembled a topographic map. I love geology, so it really stuck with me, and I made my first ZIA in that style.
This was done on a sheet of 8.5x11 cardstock (acid free) with a Staedtler pen using the tangles tipple, hibred, cadent, zingiber, and hurry