The D-Day staging areas (or “marshalling areas”) were known as “sausage camps” because they were indicated on some maps by sausage-shaped blobs. They were often situated in wooded areas that offered some concealment from aerial surveillance as hundreds of thousands of men and tons of materiél were pouring into Southern England 24 hours a day in advance of the Channel crossing. These wooded areas sometimes had temporary hutments erected in them, as well as quickly laid tarmac road systems to carry vehicular traffic and provide a handy conduit for inter-camp telephone cables. Most just had pyramidal tents.
The sausages were apparently the brain-child of a Colonel Wyman. The key aspects of his “sausage plan” were as follows:
the assembly areas were to be built around secondary paved roads
the actual areas were to be as wooded as possible to prevent detection of the troop concentrations from the air
the roads were to be blocked off to all civilian traffic
the roads were to be used as hard standings to load and unload the men and supplies
tents were to be the main billets and were to be located along the edge of the roads to expedite loading and unloading
Source: The most excellent website Skylighters.org