GIS is a broad term that can refer to a number of different technologies, processes, and methods. It is attached to many operations and has many applications . we are working on engineering, planning, management with in gis.For that reason, GIS and location intelligence applications can be the foundation for location-enabled services for analysis and visualization. CGIS was an improvement over computer mapping applications as it provided capabilities for overlay, measurement, and digitizing/scanning. It supported a national coordinate system that spanned the continent, coded lines as arcs having a true embedded topology and it stored the attribute and locational information in separate files. The most common method of data creation is digitization, a map or survey plan is transferred into a digital medium through the use of a CAD program. Modern GIS technologies use digital information, for which various digitized data creation methods are used. GIS data represents real objects such as roads, elevation, trees, with digital data determining the mix. Real objects can be divided into two abstractions: discrete objects and continuous fields such as rainfall elevations.
GIS can recognize and analyze the spatial relationships that exist within digitally stored spatial data Topological relationships between geometric entities traditionally include adjacency (what adjoins what), containment (what encloses what), and proximity.
Analysis of a digital elevation model (DEM) involves calculation of slope and aspect, DEMs are very useful for hydrological analysis. Slope and aspect can then be used to determine direction of surface runoff, and hence flow accumulation for the formation of streams, rivers and lakes.
Geometric networks are linear networks of objects that can be used to represent interconnected features, and to perform special spatial analysis on them. A geometric network is composed of edges, which are connected at junction points, similar to graphs in mathematics and computer science.
Cartographic modeling refers to a process where several thematic layers of the same area are produced, processed, and analyzed. Tomlin used raster layers, but the overlay method can be used more generally.