I am not a big time tourney angler, just like to fun fish for bass but I do go after walleye and crappie aggressively. I am looking at a Garmin Striker 5cv combo unit. It has chirp and gps. My question is about it's gps. The unit I am looking at comes with chart plotting but it's a blank white screen for plotting only, it has no maps. I can't find any info anywhere if it had an sd slot so I can upload maps. Does anyone know anything about this on this unit, and is it a good intermediate unit? Thanks.