Image maps, or client side image (CSIM) as they are known is fully supported in JpGraph. It gives you the opportunity to create hot-spots in the graphs which allows you to build a set of "drill-down" graphs.
In the following section is based on the assumption that the reader is familiar with the basic concepts of client side image map in HTML.
To shortly recapitulate. Client side image maps consists of two parts. The first part is the actual image and the second part is a mapping that gives the coordinates for areas in the image which should be marked as hot spots (i.e. click-able by the user). The library can automatically generate these coordinate maps from a given graph.
Through out the manual areas of the graph that may be used as a hotspot is given in conjuction with the general description of that area.