You'll be able to see single fish, schools of fish, bottom composition, whether soft or rocky, thermoclines ( a significant change in water temperature), weeds, most structures (stumps, wrecks, drop offs, mounds), and more. You may choose added features to provide surface water temperature, speed, barometric pressure, and location (GPS). With GPS, you'll be able to go directly back to the same hot fishing spot, no matter the lake, river, or ocean. Most fishfinders with GPS will allow you to mark hundreds or thousands of spots. The GPS uses radio signals from satellites to calculate your exact position but unlike satellite tv there is no subscription fee - it's free. And you can find your way home again - even when you lose sight of shore.