Introduction to the C-MAP application

This is the second of five articles on the use of electronic navigation applications. It focuses on the C-MAP application. The other texts cover the use of OpenCPN, Savy Navy, Navionics and SEAIQ. It focuses mainly on installations on tablets or cellular devices that are not connected to a sailboat’s instruments.

If you haven’t already done so, it’s a good idea to read the text distinguishing electronic chart formats. It’s also a good idea to read the “General information on electronic navigation applications” section of the Navionics text. It is helpful to make good use of any navigation applications.

In this text, I show you how to use C-MAP for the most important navigation tasks, namely:

1. obtaining electronic charts
2. read chart symbols.
3. measure distances and angles.
4. find out about currents and tides.
5. evaluate speed and course over ground.
6. plan and execute routes.
7. exchange planned routes.
8. record the actual route taken.

C-MAP

C-MAP is an application for illustrating electronic navigation charts. It’s available from the Apple store, the Google store and works straight out of the box on most tablets and smartphones. Of course, you’ll need a touch screen to use it, as well as a GPS.

C-MAP offers up-to-date professional marine charts for an annual subscription fee. By paying a subscription fee for a given region, the application offers maps that are continually updated (as long as your device is connected to the Internet). In 2025, the subscription price for Canadian maps was $70. It offers a 14-day trial period. After that, billing begins.

The most important added value of the C-MAP application is that it provides the option of displaying charts in the format provided by the Canadian Hydrographic Society (in the chart display options). If this option is selected, the symbols on the chart will correspond exactly to those described in Chart #1 of Canada. Users of some chartplotters will also recognize a known chart format, as this is usually the application chosen by some manufacturers to display electronic charts.

Obtaining electronic charts

To purchase charts, you first need to register by adding an e-mail address and password, accept the terms of use, and provide your payment details. The charts will then be displayed automatically on the home screen (e.g. image at the beginning of this text).

It is also possible to download maps in advance to prepare for navigation without an Internet connection. To do this, go to the “offline maps” section, choose the navigation zone you’re interested in, then click on “download”. This allows you to download in advance the areas where you plan to have no cellular (or internet) connection, enabling you to navigate in complete safety. The two images below summarize the steps involved.

Reading map symbols

To identify symbols on a chart, tap directly on the object of interest. A crosshair should then appear on the object giving basic information. Notably, C-MAP does not allow you to obtain bathymetry information by tapping on any region of the water. You have to rely on the depths displayed on the map. C-MAP therefore employs a conservative approach and is careful not to interpolate depths outside the information displayed.

Here’s an example of how to read a symbol on the chart with buoy H93. Tapping on the buoy displays the partial information pop-up window. Tapping on the “special mark details” button then displays detailed information on the object.

Correspondence with the Book of Lights, Buoys and Fog Signals

Note its reference number (ATL 1874), which enables it to be found in the Book of Lights, Buoys and Fog Signals. The application does not provide complete information on the buoy. In particular, the book shows the buoy is seasonal.

Measuring distances and angles

To measure distances and angles, use the “Plan” button at the bottom center of the screen. Tap on the “Measure distances” button to access the measurement tool. When you do so, a target is displayed, which you must move to the starting point of the distance measurement. Then press the “Add point” button.

A special feature of C-MAP is that you can add as many measurement segments as you like. You can add as many points as you like, generating a route with angles and distances. C-MAP then displays the distances between each point and the angles as readings in true degrees.

The readings are displayed as the segments would be navigated in the order in which they were added. An example can be seen in the image on the right below: the distance measured on the constructed road is 9.72 kilometers and the road segments are at 325 degrees, 331 degrees, 20 degrees and 49 degrees respectively.

To the best of my knowledge, it is not possible to display distances in units different than depths. Therefore, if you want the depths in meters, you must also have the distances in (kilo)meters. This requires some mental calculation, as by default, speeds are displayed in knots.

Learn about currents and tides

Tides

C-MAP reproduces information from federal government tide stations. To find the tide at a location of interest, you need to find the nearest station. In C-MAP, each station is represented by a pink rectangle filling up in blue (rising tide), and emptying in red (falling tide).

You can view summary tide information by tapping on a station, then obtain the complete tide curve by tapping on the “tide details” button. You can then move the cursor to see the tidal height at a given time. Tides are given at the times of the device supporting the application.

Below is an example for the Tadoussac tide station. The image on the left shows the tide station. The central image shows the partial information displayed after tapping on the station. You can see the time of high and low tide. By tapping on the “Tide details” button, you can see a graph of the tide’s evolution as a function of time.

C-MAP doesn’t allow you to change the tide date via a dedicated menu to evaluate later dates. You therefore have to scroll the tide for a long time to reach a future date.

Currents

To the best of my knowledge, the application does not allow you to find out about currents, unless you purchase a dedicated SD card. This is possible on chartplotters, but not on tablets and smartphones. This is certainly a major shortcoming of the application.

Speed and course evaluation against the background

As soon as the application receives information from the GPS, the “navigate” menu in the bottom right-hand corner will automatically display position, speed over ground and course over ground. Briefly, speed over ground is the boat’s speed relative to land. It differs from the speed indicated on a log, which measures speed relative to the water. Similarly, course over ground indicates the direction in which the ship is heading, as opposed to where the ship is pointing (course).

On the chart, the ship’s position is represented by a black arrow surrounded by a circle.

The circle represents the quality of the GPS position (the horizontal dilution of position, or HDOP). The smaller the circle, the greater the GPS accuracy.

Speed over ground is displayed at the top left of the screen. In the image on the left, the ship is travelling at 9.23 knots (nod).

Course over ground is displayed at the top center (in true degrees). In the image, the course is 048 degrees true.

It is also represented on the chart by a long blue line extending from the position arrow.

Planning and executing routes

C-MAP lets you plan routes using waypoints. In this way, you can plan a route and then execute it. Go to the “Plan” tab, then click on the “Create route” menu (see image on left).

In C-MAP, route creation begins by identifying the starting point, then the destination. Once this information has been entered, C-MAP automatically calculates a route between the two points. This route is based solely on the depth limits defined as safe in the application preferences. It takes no account of other risks or warnings that safe navigation may require.

The idea is illustrated below, in the center image, where I’ve created a route between Ile au Pot de vie and Tadoussac simply by entering the start and end points. C-MAP then takes me through the shallows, out of the channel and close to the typical lapping of the Fjord entrance. Anyone who finds this route tempting should read the sailing instructions on the particularities of the currents at the entrance to the Fjord! It’s not a good idea, and it’s an excellent illustration of why a minimal path algorithm is no substitute for marine judgment.

So, to improve the route proposed by C-MAP, you need to add intermediate waypoints (image on the right, above). Waypoints are added in sequential order, starting from the beginning. Thus, the first waypoint added is implicitly the one after the starting point, the second after the first, and so on. Adding waypoints greatly improves safety compared to the initial route. A route with intermediate waypoints is shown in the image on the left.

Once a route has been created, it can be executed or saved. In run mode (right image below), the route is displayed with the ship’s navigation information. In particular, you can compare the route on the ship’s bottom with the planned route, and make the appropriate corrections to follow the route.

Exchanging previously planned routes

C-MAP lets you download routes from other navigation applications. Similarly, it allows you to export routes to other applications. The exchange format is .gpx. It’s an open format that enables routes to be shared.

To export a route, select it from the routes already saved (left-hand image below), then choose the export option (right-hand image below). The application will then create a .gpx file on your electronic device, which you can then share.

Note that there is a “share” option in the route sharing options. If this option is selected, C-MAP will create a link which can be shared, but which will require the recipient to install C-MAP before accessing the route. On the other hand, the .gpx file can be read by most navigation applications.

To download a route that someone shared with you, simply open the .gpx file forwarded to you. The action will open C-MAP and display the route. If you have more than one e-navigation application on your device, it’s possible that the action will open an application other than C-MAP. In this case, you need to modify your operating system preferences to indicate which application should be used.

Record the actual route taken

The track is activated via the navigation menu. Simply tap on the “Activate track” button and the application will start recording your position on the map. The central image below shows a track recorded over the course of an hour. It shows a ship taking the traverse du lièvre and then the Chenal du sud on the St. Lawrence River (note that the maneuver is carried out at high tide!)

The image on the right serves only to illustrate that the application records the position of the electronic device. If the device is in a person’s pocket and that person is walking on the ship, the track will show the person’s movements on the ship. These “zig-zags” have nothing to do with GPS inaccuracy, but rather that the electronic device was moving on the ship!

Conclusion

C-MAP is a navigation application that allows you to perform most of the common navigational tasks. Its greatest strength is its ability to display charts in ENC format, a standard known to the merchant navy. It is also the default software application for many chartplotters.

Note that it is not possible to analyze currents within the application, and its automatic route construction method is, for the uninitiated, dangerous. I’ll also report on my own unpleasant experience of the application crashing continuously during use.

That said, I also know people who swear by this application. It includes a lot of information and tools for making passage plans.