A shapefile is a storage format for geographic data. Shapefiles can contain lines, points, polylines and polygons that represent different features on a map.
Each shapefile must contain at least three files – .shp, .shx, and .dbf. The .shp file contains the actual geometry data (e.g. points or lines). The .shx file contains a index to find the information (kind of like a reference for looking up data). The .dbf file contains attribute information (a table with more info about each feature). The image on the left shows two shapefile layers (green “storm sewers” and red “drainage areas”).