This was the original technique used for image mapping. The maps are processed by interaction with the Web server. The information for the image map's links is stored in a map file on the server. When the user clicks on the 'hot spot' the Web server then interprets the information by transferring the coordinates of the click to a program running on the Web server. The program examines the data and determines the URL link. The way the maps are stored is dependent on the software being used on the server. Maps are usually stored in text files and the two most common forms of the standards for storing these are NCSA and CERN.
The only advantage to using server-side image maps is that any browser should successfully interpret them.
There is a fair amount of processing time involved - when the user clicks on a hot spot, the client must establish another connection to the server, and then pass the coordinates back to the server to be interpreted; the server must then return the URL to load next. The format of the map file also needs to be considered, based upon the configuration of the server where it will be stored, whether it is an NCSA or CERN-style server.
When the user passes the pointer over the image, the co-ordinates - rather than the URL will be seen on the toolbar at the bottom of the screen.