Location of Nigerian Ethnic Groups

Nigeria has about 250-300 ethnic groups as measured by self-identification or the presence of different languages.  This map shows the general location of some of the major centers of the more numerous groups.  Obviously the Igbo had spread out of the southeast into the other regions of Nigeria but their "home region" was in the southeast.  What conclusions can you draw from this map?  Is there a clear cut Igbo-only region in Nigeria?  Were the Hausa spread extensively and exclusively across northern Nigeria? 

Nigeria Ethnic Groups