Well, for me, I don't know for certain. I just got a fish finder which I'll try to learn how to use this year, but I haven't been using one. I do fish shallow, 15 ft or less, like 90% of the time. I just take an educated guess based on all the data I have. Its more like based on everything I know (water and air temp and the trend for the past week, time of the year, wind speed and direction, sun angle, time of day, current from inlet streams or the current by the dam, forage base, topography of that body of water, etc) I try to eliminate 80% of the lake, and find my most productive areas on a map, and then when I hit the water, I'll go to those spots and fish them thoroughly, knowing odds are really high they have to be there somewhere, and some of those fish are going to want to eat. If I've fished a lake a lot, I dont really do this because I already have a really good idea where the fish are. Its too much to go into on here, but what really helped me out was watching on youtube a lot of Bassresource. They have some videos where they really go in depth of finding and patterning fish, their habits, how to break down a lake or pond, etc. Spending more time watching every video about it that I could, and learning about the habits of bass has helped me far more than learning about lures and how to fish them. I fell in love with bass fishing for its mental challenge. Its not just about going out randomly casting lures, hoping for the best. Its about correctly analyzing all the data around me, to come up with an educated guess on where the fish might be. I don't always do it correctly, but when I do, it helps develop that gut feeling where it gets easier over time to predict where the fish will be. I have passed up some pads that I thought didn't have good odds of holding fish, just to have a guy pull the winning fish from it a few minutes later. I don't think anyone ever knows for certain where fish will be. We all guess, but for some, its a more educated guess than a wild guess. Hope that helps.