Read Latitude And Longitude On a Nautical Chart

How to Read Latitude And Longitude On a Nautical Chart? A Beginners Guide to Chart Calculations


Nautical charts are detailed maps that are used by sailors to navigate the seas and other waters. These charts contain a wealth of information, including water depths, shoreline features, navigational hazards, and much more.

Understanding latitude and longitude on a nautical chart is crucial for safe and accurate navigation. Latitude and longitude are used to pinpoint a vessel's location, plot a course, and avoid obstacles.

Latitude and Longitude Defined

Definition of Latitude

Latitude is a measure of how far north or south of the equator a location is. It is measured in degrees, minutes, and seconds, with the equator being 0 degrees and the poles being 90 degrees.

Definition of Longitude

Longitude is a measure of how far east or west of the Prime Meridian a location is. It is also measured in degrees, minutes, and seconds, with the Prime Meridian being 0 degrees and the International Date Line being 180 degrees.

Compass rose from a Nautical Chart

Working with Latitude and Longitude on a Nautical Chart

Finding and Measuring Lat and Long

When navigating with a nautical chart, you'll need to understand how to find and measure latitude and longitude. These coordinates are measured using a grid system of horizontal and vertical lines, known as graticule lines. By identifying these lines, you can locate any point on the chart with precision. Remember, the vertical lines represent longitude, while the horizontal lines represent latitude. The graticule lines are labeled with degree marks and numbered and lettered to help you quickly identify specific coordinates.

Understand the coordinate system

To read latitude and longitude on a nautical chart, it is essential to understand the coordinate system and how it works. Once you understand how the graticule lines are labeled and spaced, you can start to interpret the coordinates.

Use the compass rose

The compass rose is a circular diagram that is used to indicate the orientation of the chart. By using the compass rose, you can determine the direction of north, south, east, and west on the chart, which is crucial for navigation.

Pay attention to the scale of the chart

The scale of the chart tells you how much the chart has been reduced from its actual size. By understanding the scale, you can calculate the actual distance between two points on the chart.

Look for landmarks

Landmarks such as islands, rocks, and buoys can be used to pinpoint your location on the chart. By identifying these landmarks and comparing them to the chart, you can determine your position and plot a course to steer.

Practice reading and interpreting nautical charts

The more you practice reading and interpreting nautical charts, the better you will become. It takes time and practice to develop the skills and knowledge needed to navigate the seas safely and accurately. A good place to start is to pick random locations on the chart and try to accurately measure their position in terms of latitude and longitude. 

marine map with dividers

Common Mistakes When Reading Latitude and Longitude on a Nautical Chart

Misinterpretation of Numbers

Misinterpreting the numbers on the chart can lead to errors in navigation. It is important to take the time to carefully read and interpret the coordinates to avoid mistakes. A single incorrect digit can have you miles from where you actually are which could be serious if communicating your location in any kind of emergency. 

Confusing Latitude and Longitude Coordinates

Confusing latitude and longitude coordinates is another common mistake. It is important to remember that latitude coordinates are listed first, followed by longitude coordinates.

Not accounting for the scale and projection of the chart

The scale and projection of the chart can affect the accuracy of your navigation. It is essential to understand how the chart has been scaled and projected to ensure that your calculations are accurate.

Overlooking important symbols or details

Nautical charts contain a wealth of information, including navigational symbols, landmarks, and other details. It is important not to overlook any important information that could affect your navigation.

Nautical chart with waterproof cover on deck

Additional Tips for Accurate Reading of Latitude and Longitude on a Nautical Chart

Use a magnifying glass

A magnifying glass can help you read the small print and details on a nautical chart, making it easier to interpret the coordinates.

Double-check your calculations

Double-checking your calculations can help you catch any errors before they lead to navigational mistakes. 

Consult with a professional

If you are new to boating and/or reading nautical charts, it is always a good idea to consult with a professional for guidance and advice. Start by running showing your calculations to someone with experience and see if you are doing it the right way. 

Use digital tools for accuracy and ease of use

There are many digital tools available today that can help you read and interpret nautical charts more accurately and with greater ease. One such tool that can greatly aid in this process is the boating app savvy navvy (shameless plug). This app provides a wealth of information and features that can make reading nautical charts a breeze.

Firstly, savvy navvy offers high-contrast charts that are based on official hydrographic office charts from around the globe. The app designers have customized the charts to display essential marine information in a clean and easy-to-view interface. The charts are also equipped with a detailed wind direction map and tidal graph overlays, allowing users to quickly check the wind direction, speed, and tidal conditions for their location.

savvy navvy offers a variety of additional navigational tools, including GPS active tracking, which allows users to view their live position and check their Course Over Ground (COG) and Speed Over Ground (SOG) instantly. This feature helps boaters to quickly determine their distance from key features around them, as well as plot their course with ease.


Navigating the vast and unpredictable waters can be a daunting challenge in the beginning, but with the right skills and knowledge, you can conquer it with ease. Reading latitude and longitude on nautical charts is a vital skill for any boater, as it helps to ensure safe and accurate navigation. Remember to use the compass rose, pay attention to the scale of the chart, look for landmarks, and practice reading and interpreting nautical charts to become a master at it. In the beginning, it is important to practice your chart readings as much as possible, as this will allow you to navigate with confidence, unlocking new adventures and discoveries along the way. While we always recommend knowing how to read a traditional nautical chart (paper will always be your backup if anything happens to your digital equipment), consider downloading a boating app such as savvy navvy to simplify your boating navigation and save time with future measurements and calculations. 

savvy navvy, the boating app that brings all essential marine information together in one place. Featuring global charts, wind and weather forecasts, tidal graphs, GPS Tracking, automatic weather routing, and marina and anchorage information. It’s like Google Maps for boats.

Inspired to get on the water? Start your free trial today.