Isopach

http://www.google.com/imgres?hl=en&biw=1280&bih=662&tbm=isch&tbnid=JIFIE1Pi7CbSVM:&imgrefurl=http://www.glossary.oilfield.slb.com/DisplayImage.cfm%3FID%3D114&docid=XiNlNig2zerfyM&imgurl=http://www.glossary.oilfield.slb.com/files/OGL98135.gif&w=600&h=387&ei=jiFJUIPCFZKK9gTUsYDwBQ&zoom=1&iact=hc&vpx=174&vpy=161&dur=39&hovh=180&hovw=280&tx=124&ty=83&sig=104655054681110617605&page=1&tbnh=123&tbnw=191&start=0&ndsp=17&ved=1t:429,r:0,s:0,i:73

Isopach
Isopach is a line on a map or diagram connecting points beneath which a particular stratum or group of strata has the same thicknes.