Since Helfa wants to include the entirety of the people and thus also cover everything there is in interesting areas, a flat hierarchy would become too confusing. Topic groups also have a hierarchy, so that they can be found better. So there is a general topic that can then have subtopics, which in turn can have subtopics, and so on.

For example, the Nature topic has Conservation, Forest, and Planting as subtopics. For planting, the sub-themes could be arable land, allotments, parks ... etc. Each topic in turn has different levels, as they can be made in all groups. The sole purpose of these hierarchies is to distribute the information in several or single groups, if necessary. So people who are generally interested in nature will be informed about a possible meeting in the same way as permaculture people and those who are interested in parks (theme group hierarchy all themes from the theme nature, all the way down, but only the local groups that are registered near the meeting place). On the other hand, a seminar that is only about permaculture can be limited to this group, while all local groups are addressed globally (with the same language of course)