CAD and GIS are both technology related to mapping and spatial dimensions of earth surface objects. CAD mainly is used in the Architecture or civil engineering domain (microscale) and GIS is used for spatial analysis at the landscape/regional level. Both of the technology are using spatial representation in vector graphics structures. The format for these vector data is various, but DWG is a major format in CAD since decades ago, and Shapefile/SHP is the major and most used spatial data format in GIS for at least since the nineties. Because both of them are using vector graphics, straight conversion between two mainstream formats is absolutely possible. Modern CAD software mostly supports direct reading of SHP format and vice versa. CAD also has point representation, polyline representation, and polygon representation as well as Shapefile GIS format. There are no many differences between those two formats. The only difference is CAD DWG format usually didn't store tabular informat...
