GEM (Geographically explicit Event Model) is a method for phylogenetic biogeography to infer both biogeographic events (vicariance, full copy sympatry, point sympatry, and founder event) and geographic ranges at the internal nodes of a tree, if you have the explicit geographic ranges of the terminals.
GEM is based on Hovenkamp's ideas [1, 2] on using explicit distribution ranges in biogeography, on Ronquist's DIVA  on using and scoring events, as well as in the implementation of the Spatial analysis of vicariance , on geographic data models and algorithm mechanics.
It provides further development of the ideas presented in , and supersedes my older program, VIP
GEM is implementated in two pilot programs available as Windows and Linux executables, as well in source code (available under BSD-2 license).
 Hovenkamp, P. 1997. Vicariance events, not areas, should be
used in biogeographical analysis. Cladistics 13: 67. DOI:
 Hovenkamp, P. 2001. A direct method for the analysis of vicariance patterns. Cladistics 17: 260. DOI: 10.1006/clad.2001.0176.
 Ronquist, F. 1997. Dispersal-Vicariance Analysis: A new approach to the quatification of historical biogeography. Systematic Biology 46: 195-203. DOI: 10.1093/sysbio/46.1.195.
 Arias, J.S., Szumik, C.A., Goloboff, P.A. 2011. Spatial analysis of vicariance: A method for using direct geographical information in historical biogeography. Cladistics 27: 617-628. DOI: 10.1111/j.1096-0031.2011.00353.x.