Although these terms sound similar, they are slightly different. An area that is a flood plain is an area where a river or stream crests regularly and floods the area on either side of the waterway. This leaves a flat, sediment rich area that often contains high mineral nutrients and can be easily seen. A flood prone area is one that may or may not be within a water body's regular flood plain, but will occasionally flood as waters rise. These areas may also be at the bottom of hills away from water bodies but are topographically capable of pooling water from runoff. Only a fool would build on a known floodplain. These areas flood on a regular basis as the seasonal levels of streams rise and fall. Many civilizations over the last three-millenium have built on these plains for convenience and did not take flood years into consideration. A common tool is the fifty-year or hundred-year flood mark. This is the area that can be expected to flood should a river crest at a given height. The fifty-year or hundred-year designation states the highest known cresting level in the last 50 years or 100 years or whatever number of years chosen. A builder has to do a risk assessment to determine at what flood level would it be safe to build. GIS is capable of gathering this information and including it on a layer. For simplicity sake, we chose to have this information included on a hydrologic layer, which includes all streams, rivers and wetlands.