Down Imaging vs. Side Imaging on Fish Finder

The main difference between down imaging and side imaging is that down imaging scans vertically and side imaging scans horizontally.

If a little tongue in cheek, here’s my take on down imaging vs. side imaging on a fish finder. Firstly, neither are necessary for catching fish.

Even commercial fishers use their knowledge of the ocean, experience, and knowledge of fish behavior before using machines.

However, depending on where you’re fishing and for what, they will increase your chances of catching fish. 

Put very crudely, down imaging is useful inshore and offshore, whereas side imaging is great for inshore applications.

Let’s unpack this a little with some easy definitions and explanations. We’ll not get hung up on technical stuff here. I want to give you the basics without adding any confusing tech babble.

Our goal in this article is not to provide a firm recommendation on sounders, but rather to give you the tools you need to ask dealers and experts the right questions, while being able to understand how they respond.

What’s the Difference Between Down Imaging and Side Imaging

As mentioned, the main difference between down imaging and side imaging is that down imaging scans vertically and side imaging scans horizontally.

The down imaging (DI) scans directly underneath your boat, taking in a forward and back portion of the subsurface. 

Side imaging (SI) covers the water on either side of your boat.

Comparing the two is not comparing apples with apples, neither is one better than the other. It’s more a case of both types having fishing application advantages and disadvantages.

man holding a fish finder in front of a lake sunset

Here’s a basic application scenario to illustrate. 

Side-scanning is great when fishing rivers and creeks in shallow water around 10 to 15 feet deep, casting into cover towards the banks.

If you’re fishing deeper, vast bodies of water, especially open waters, looking for deeper reefs and fish-holding structures, you should use down imaging. 

You can scan at pace, covering plenty of areas in search of fish-holding cover and structure.

When selecting a fish finder, you should consider the fishing that you do. 

If you fish shallow rivers and creeks exclusively, casting toward the banks, you will benefit from side scan imaging.

Here are some good side imaging options

If you fish creeks, rivers, and open waters, you have a compelling argument for both. However, if only one was an option, you’d probably go for down imaging.

For the open waters angler, down imaging is going to be most effective because it is superior at depths.

The problem will be the budget. You can throw plenty of cash at these guys, so if you’re on a tight budget will you go one or the other, or a unit capable of both?

A further variable lies in the capabilities of the unit that you purchase, regardless of the type.

For example, are you better placed to get a top-shelf model of either, or a basic version of both? Again, this will come down to your fishing habits and applications.

Understanding your application against the pros and cons of each sounder type leads to better choices.

See Also: Is Side Imaging Worth The Extra Money?

Advantages of Down Imaging

  • Down imaging sounder is the most effective at scanning deep waters. With most of the planet covered in deep water, you’re better placed for finding more fish.
  • DI delivers sharper, more detailed pictures when you’re moving at speed. Fishing open water costs a lot of fuel, time, and therefore money to find fish-holding structures over vast areas. You want to be able to locate likely target areas quickly. Down Imaging provides for this.
  • For those on the tightest budgets, entry-level down imaging sonars are generally more affordable than side imaging. When even basic subsurface information can provide you with a fishing advantage, having a basic DI will have value-add wherever you fish.

Disadvantages of Down Imaging

The only real disadvantage to down imaging is that your fishing application is so SI-specific that it provides you with little useful insight. 

For example, if you cast, flip and pitch at banks 20 to 50 yards away, DI won’t tell you much about the target zone. 

Beyond this, there isn’t really any disadvantage to owning a Down Imaging sounder.

Even the cheapest DI sounder provides useful information about sea/river/creek bed features and geography. 

This information is valuable to anglers who understand fish behavior relative to habitat.

close-up shot of a person spinning a fishing reel

Advantages of Side Imaging

  • The big advantage that many river and creek anglers love is that you can scan both sides of the river. With a wide enough reach, or narrow enough river, you benefit from finding targets on either side of you. This is a huge benefit.
  • Most SI is a premium addition to a DI. The ability to switch between SI and DI images is as good as it gets, particularly with hi-resolution images from a wide cast scan. This top-shelf option tells you nearly everything there is to know to maximize your chances of locating fish.
  • The image quality of top-shelf SI sounders is breathtaking. You know little is being left to guesswork when you can see the rusted rowlocks of a sunken rowboat 30 feet from your boat in 15 feet of water on your display.
  • Anglers spend a lot of time casting at the structure around banks. Only side imaging gives you a perfect view of your target zone.

 Disadvantages of Side Imaging

  • Side imaging sonar tells you little about what’s happening directly underneath your boat. However, you can change your course, moving wider to bring what was previously under the boat into scan range – so there are workarounds.
  • Sometimes there’s no substitute for the ability to pick up detail at depth. However, most side imaging units will be an add-on to a DI, so you will have this capability anyway.
  • Side Imaging software and added transducers are expensive, as are the monitors that allow you to maximize the resolution of the features scanned. SI isn’t cheap and can take a little bit of education to ensure you maximize performance.
  • Side scanners don’t work to deliver sharp images at speed. And slow boat speeds add to the time it takes to find likely target zones.

See Also: Best Portable Fish Finder for Bank Fishing

Frequently Asked Question

Side Imaging vs Down Imaging for Trolling?

Down imaging and side imagingI are used differently when trolling. It all depends on whether we’re in open waters fishing the depths offshore or inshore trolling a shallow river bank.

If you ‘re offshore down imaging is great for keeping the boat over the target area and finding it in the first place. 

For example. If you’re fishing the edge of a shelf, your DI locates the desired contours quickly, and you can identify and keep a trolling pattern within the strike zone – at speed.

Side Imaging works very well at slow trolling speeds which are ideal for rivers and creeks. You can identify your run with great detail, and even troll both sides of the boat.

Offshore, side imaging can help when you’re trolling close to the shoreline (usually ocean rocks), as it can identify depth changes, features, and the surface monsters you’re chasing.

What Does Down Imaging Sonar and Side Image Sonar Mean?

Down imaging sonar is a system that emits sound waves vertically down beneath the boat. 

The sound waves bounce off structures and features such as weeds, rocks, and fish, with a computer deciphering the raw data into images we can use to identify sub-surface features.

Side imaging sonar uses the same basic principles as down imaging sonar. 

The difference is the direction in which the sound waves are projected. As the name suggests, side imaging sonar waves are directed to the side of the boat, not directly down.

Should I Use Side Imaging or Down Imaging on a Kayak?

This is an interesting question for which I see plenty of presumptuous answers. In truth, the vessel from which you fish has little to nothing to do with your choice of sonar.

Your choice of sonar will be determined by the type of fishing that you do. 

For example, if you Kayak offshore, or nearshore, fishing the depths directly under you, then down imaging is best.

If you fish the rivers drifting and trolling, casting at the banks, then side imaging may well be the better option for you.

Can You Use Side Imaging Sonar to Pick up on Structure?

The answer is yes, side imaging can pick up on structure. With a top-shelf sonar device, you can see outstanding detail. 

While all good sonar will identify fish, the critical feature of sonar is that it will identify the cover and structure where fish live.

You can walk down a suburban street and see nobody. 

However, you know they must be there because you can see the places that people live – their houses. It’s the same with fish.

Fish live and congregate around structure and cover, just like people. Find the structure and cover with your sounder, and you’ll likely find the fish who live there.

Is Side Imaging Worth the Extra Money?

Value is relative and subjective. I can’t answer this question effectively. 

What I can say is that if you fish the river banks for bass, and troll the shoreline around any inshore body of water, you will definitely find side imaging particularly useful.

If money is no barrier, of course, get it. It’s no load to carry and will provide you with a complete image of the area you’re fishing.

However, if you’re on the tightest of budgets, hang on to your hard-earned money. You won’t be lost without it. 

A basic down imaging sounder that won’t hurt your wallet will provide you with some great basic subsurface information, regardless of where you fish – and you WILL find it useful.

Side imaging is great – no doubt. However, my first course of action, relative to sounders and budget, is to cover under the boat first.

Ultimately, however, these gadgets, awesome as they are at revealing the secrets of the underwater world, aren’t essential for catching great fish, and plenty of them. 

The best weapon is your fishing habitat knowledge.

Spend what you can afford. Sounders are fantastic, both side imaging and down imaging are worth every dollar you can safely invest. 

See Also: How To Read a Fishfinder Screen

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Sean Ward

Hey there, my name is Sean – OnTrack Fishing is my site. I’m based in the UK yet I’ve been fortunate enough to catch bass in the States, barramundi in Australia, trout here at home and carp on the Danube delta. If I’m not fishing, or talking about fishing, then….I’m probably asleep.


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