DOQQ

http://www.google.com/imgres?num=10&hl=en&biw=1280&bih=681&tbm=isch&tbnid=TzlRTsuLLnj6hM:&imgrefurl=http://www.utexas.edu/depts/grg/hudson/grg360g/EGIS/final_project/spring04_projects/web_justin_reynolds/Lake%2520Travis.htm&docid=_m--96gsbE-F-M&imgurl=http://www.utexas.edu/depts/grg/hudson/grg360g/EGIS/final_project/spring04_projects/web_justin_reynolds/Lake%252520Travis_files/blue_Travis_doqq.jpg&w=350&h=299&ei=drUTT8rIE4uWtwfRqOyRAg&zoom=1&iact=hc&vpx=424&vpy=156&dur=701&hovh=207&hovw=243&tx=130&ty=124&sig=106376105954718851060&sqi=2&page=1&tbnh=160&tbnw=201&start=0&ndsp=15&ved=1t:429,r:1,s:0

This is a DOQQ map. As you can tell there are a lot of squares on the map dividing this image into regions. DOQQ stands for Digital Orthophoto Quarter Quads. It would be used for dividing projects into simpler segments.