Recently I have been looking into the specifications for the Open Geospatial Consortium (OGC) Web Feature Services (WFS) that provide a standard interface between geographic information systems (GIS) for the transfer of geodata.
I've been starting to think about it in terms of using the Drupal web framework as a geodata store that can be used by any standards compliant GIS. Drupal can already be considered a Geospatial Content Management System (GeoCMS) so this seems like a natural extension to allow other systems to talk to it.
In GIS, the term 'layer' is usually used to group together geographic information relating to the same kind of feature, e.g. forests, places or roads. These are often stored in different files or different tables in a database. In Drupal the equivalent concept is a little more flexible and fine-grained. All of the information is stored in one place (with the ability to extend a basic piece of information with extra attributes) and can be filtered by any number of 'tags' that may be assigned to different pieces of information.
Using a WFS server as an interface to data held in Drupal would mean that systems would have access to any number of geographic datasets simply by combining tags to retrieve the data that they need.
I'm looking forward to putting more work into building up a spec for a WFS Server module for Drupal, and hopefully one day geographic information systems will be able to query Drupal for dynamic geodata, and even create, update and delete it as well.