Functionality GISs are spatial analysis engines. This is what differentiates them from all other data handling capabilities. The functionality they need to offer must be based on the demand for analysis.
Geographical analysis requires a spectrum of capabilities ranging from simple to complex.
The current set of functionality provided by commercial GIS software products covers the middle of this spectrum. The most desirable future developments in this middle section will be the focused provision of functionality tailored for specific types of users. The ends of the functionality spectrum are where new GIS development will make the most societal impact. GIS functionality needs to have the ability of modeling processes that will allow the behavior of complex spatial systems to be examined, leading to the ability to predict outcomes and, above all, to understand them. It is debatable whether this functionality should be developed by the GIS industry, but it represents the strongest GIS development resource in the world and may be the only capable agency.