Where do the developers in my FOSS community live? For large open source communities where personal contact with developers is impossible, answering this simple question may be difficult.
Fortunately, there is an approach that, even when it does not produce a great deal of detail about exact location, can be useful for visualizing how your community is spread around the world: time zone analysis. Time zones are not good for fine-grained location, but are enough to give an idea of large geographical areas.
Time zone analysis uses information provided as a byproduct when developers interact with some repositories:
Git includes local time as a part of commit records. When commits are merged in the project Git repository, the author time (which includes the time zone tag) is usually not altered. Be warned that some actions on commits may alter their time, switching to the time zone tag of the person performing the action. Still, the information is in most cases reliable enough to know about the time zones for commit authors.
Mailers provide the local time, including time zone tags, in all sent messages. In many cases, the software archiving mailing lists keep this time unaltered. In those cases, the analysis of mailing list repositories permit the identification of time zone for senders.
For some uses, this is enough. For example, the above chart about OpenStack Git authors show clearly that most of the developers are from North America and western Europe, with some participation from the Far East and other regions. The distribution of the Eclipse mail senders is even more centered in western Europe, with large participation from North America and only some presence from the rest of the world.
You can use this kind of study to track the results of policies for increasing geographical diversity, to know where developers come from, or to decide on a meeting location or chat session start time. In general, time zone analysis is a simple way to learn about the big picture of where your developers come from.