Geogen is the short form for "geographical genealogy" which means location based ancester research. On this website you can create maps which show the distribution of surnames in Germany. Significant concentrations can point to a local root of the family or of the family name.
The maps generated on this site are licensed under the Creative Common License Attribution- NonCommercial- ShareAlike 2.0 Germany. You are allowed to copy, distribute, display, and perform the work or make derivative works as long as its non-commercial and you don't remove the copyright notes. (Feel free to send me an e-mail if you need a CC-BY-SA license. Nearly all kinds of work will get this explicit permission.)