Flow maps

http://www.google.com/imgres?imgurl=http://www.groundwatersoftware.com/media/MapVPrismMap.gif&imgrefurl=http://www.groundwatersoftware.com/map_viewer.htm&usg=__6E0pBN7bUsv39yjgqfHegWi1-Xg=&h=333&w=450&sz=20&hl=en&start=126&zoom=1&tbnid=Lf02HUBEoAP6pM:&tbnh=135&tbnw=180&ei=xFkjTvCSLOOysALGxajfAw&prev=/search%3Fq%3Dflow%2Bmap%2BGIS%2Bdefinition%26hl%3Den%26safe%3Doff%26sa%3DX%26biw%3D1600%26bih%3D751%26tbm%3Disch&itbs=1&iact=hc&vpx=372&vpy=168&dur=1482&hovh=193&hovw=261&tx=165&ty=112&page=5&ndsp=32&ved=1t:429,r:1,s:126