GIS data structures are used to implement the conceptual views of spatial data (vector and raster models). The power of a GIS is dependent on the richness of information contained in the spatial data structures. Vector models are based on points, lines and areas. Raster models are based on grids. Each cell has a value that is used to represent some characteristic of that location.
Layers are used to display geographic datasets in various digital map environment. A layer stores the path to a source dataset and other layer properties, including symbology. You can use multiple layers on one map and specify its properties. Shapefiles represent spatial character of the object in terms of shape, size and spatial arrangement. Shapefile usually comprise three separate and distinct types of files (main files, index files and database tables). Data base files store additional attributed that can be joined to a shapefiles’ feature. Attribute data types supplement geographic spatial feature with additional information. Spatial data includes information of location and attribute data includes information about other characteristics (what, where and why). A legend is a visual presentation of the symbols that are used on the map with some additional explanations. It includes a sample of each symbol and a short description of the meaning.