Addar said:MY POOR ENGLISH :
1.GERALT Z RIVI-have one easy meaning "Geralt from Rivia", its old medieval form
2.Geralt Ri(w/v)ski)- first time hearing this but its adj form...it can have the same meaning like geralt z rivi but also if for example people from rivia has some distinguish them characteristic like big nose, we can say that every one who has this :"big nose " is "Rivski" so this form is not attach completely to the Landscape... in fact to me polish its sound strange and we never use this form to described where are we came from
if we know many geralts we can called them like " this gerlt , u know , "Rivski" one not "Temerski"...etc
3. Geralt Riv- is another form, use in book also, its noun describing your motherland, living in poland im Polak(Pole ),so geralt "coming form rivia" is Riv (Riw)
That's just the manner of explanation I wanted, and your English is just fine.
So, to oversimplify, "Geralt z Riwi" is literally "Geralt of Rivia" and would be used as a knightly name in older days; "Geralt Riwski" would not be used as a name, but would mean "Geralt, who has some characteristic we associate with Rivians"?