every portable Gps , Branded or non branded (but it does have a brand fo sure) have different maps like for the city, offroads etcs....

these maps get updated once in every few months or even a year due to the constructions happening on road and new places being built or even demolished.

so ur source of the map will be no where other than the Gps makers website, get the name of the brand and then find the website , if u find out there is no website for ur gps then sell it off...

if u got it from dragon mart ,then its obviosly chinese made and unluckily the website might be in chinese language and will not have english, at this point...

U TO BE IN TROUBLE