As I understand if you want DI,SI, and 2D from Humminbird or Lowrance you have to also get GPS.Since my lakes are not on it, this seems like an expensive add on. I would think smart companies would see this and make units without this feature.I have a hand held unit and can't see any uses for an additional GPS. You guys may be able to set me straight if I am off base. Also are units with external antennas better than units with built in antennas. I am considering the HB 898 unit with external antenna. since the screen will be a little larger. Comments would be appreciated Thanks everyone for any help......