looking for gps techology

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i plan to buy some gps product.but i don't know what category for good tecnology gps that i musy buy.did we know the technology first or price?actually i don't know much about good gps.as weel as i know,gps is only like map,but update and can bring us when go the trip.that' it.soo..can you tell me more,what the first thing should i do,to get a good gps technology?what merk and how much the price?should i do some selection too for get good gps.need for compare and if ok,then i will buy it.waiting your respon