Measure distance

More detail

What it is for. Use it to check how far a spot is from the inlet, how far apart two spots are, or how wide a feature on a layer is, such as an eddy. The button is in the stack of controls on the right side of the map on both the iPhone app and the website, and the two pins start out side by side in the middle of the view.

On the iPhone app. The distance shows in a small box at the top of the screen. Put a finger on a pin, hold for an instant and drag it. The box has two buttons: one brings both pins back to the middle of the screen, and one closes the tool. Tapping the ruler button again also puts the tool away.

On the website. Drag a pin with the mouse. The line between the pins is dashed, and the distance is written at the middle of the line, to two decimal places. Click the ruler button again, or press the Esc key, to put the tool away.

What it shows. The distance is shown in the unit you chose under Distance in Preferences: nautical miles, miles or kilometers. Zoom in on each end before you place its pin. It works anywhere in the world and keeps working when the ocean layers have a problem.

What it does not show. The line cuts straight across whatever lies between the pins, including a headland. It measures one leg only. The Scale bar on the website gives a rough sense of distance across the view.

When it does not respond or looks wrong. If you have moved the map and the pins are out of view, tap the first button in the box on the iPhone to bring them back. On the website, put the tool away and open it again, and the pins come back to the middle of the view.

The numbers

How often it updates	Instantly, as you drag a pin
Where it covers	Anywhere in the world
Observed or modeled	Neither. It is worked out from the two points you place
What you see on screen	A line between two pins, with the distance at the middle of the line on the website and in a box at the top of the screen on the iPhone app. Nautical miles, miles or kilometers

Source: the app itself.