A contour line is a representation of equal points of elevation. Contour lines are displayed successively in a contour map to display the change in elevation over an area. The interval between lines defines the resolution of the elevation data.
Elk Grove Village recently developed a one foot contour dataset from LiDAR (Light Detection and Ranging) data collection to improve upon a two foot contour provided by Cook County. Other datasets can be derived from this elevation information such as a Digital Elevation Model (DEM) or Digital Terrain Model (DTM) and is simply another way to simulate the real world lay of the land. These elevation representations become very powerful decision support tools when overlaid with other infrastructure such as storm sewers in a GIS (Geographic Information System).