How to Read a Topographic Map
Topographic maps, or topo maps for short, are an incredible resource for anglers. Today, nearly every lake in America has a detailed map with one-foot contours available for free on the internet, giving anglers easy access to the layout of their home water, or any other water they choose.
The topo map is the first thing you should look at before you head to the water, particularly if you’re heading somewhere you’ve never been. Bass relate to structure throughout the year. Points, humps, channel swings, ditches are all examples of structure that the bass will call home, and map study is how you find those places. Map study is important all year, especially during the prespawn migration in the Spring.
How do I read a topographic map?
A topo map uses lines known as contours to display the elevation of land, or the depth of a body of water, in an easy-to-read two-dimensional format. Contours represent a change in depth at whatever interval your specific map uses. Most common in one foot, meaning the depth changes by one foot between two contours. This means the closer the contours are together, the steeper the grade. Note the closeness of the lines near the bank on the image below of a lake’s topo map. This is a deep lake with a very steep shoreline.
Note: Usually the contours will be labeled with a number, Indicating the exact depth at that specific spot.
Many of the tools available today that provide topographic map data also employ shading to show a high-level overview of general depth, as shown below. The darker the color, the deeper the water. This is a very useful feature for anglers, particularly when you start breaking down a new lake, as it gives a quick overview of the depth across the lake.
Here are some very poor drawings of how topographic contours look in reality. The first image is a shallow flat with a deep channel that cuts through the middle of it, which you can see in the deep V shape the bottom makes in the corresponding drawing.
There are a number of different sources of topo maps that are available to anglers, and many of them are free. Navionics is available online for free at webapp.navionics.com and map cards are available for purchase for your fishfinders. Lakemaster is available exclusively for Humminbird electronics. You can purchase the maps for individual lakes online or on their app. Both of these sets of maps are created by the companies that own them. C-MAP is an open-source mapping site where anybody with a boat can record mapping data and upload to a public (or private if you have a paid account) database. The unique feature here is that small bodies of water like ponds often have maps for you to use, which is not the case with other options. It’s also the most accurate, but large bodies of water are often incomplete.