When Microsoft announced Windows Ink at its Build 2016 developer conference, the firm promised that apps such as Maps and Photos would support the feature. Due to arrive in the Anniversary Update, the features never arrived for said apps in any Insider Preview builds.
Since the Windows 10 Anniversary Update arrived today, the feature is arriving to Windows Maps just in time. As you can see from the image above, you can use it to map custom routes or to simply draw on a map. There's also a neat feature that allows you to draw a route and Maps will give you the distance.
As you can also see from this screenshot, the writing stays on the location that you wrote it on. If you move the map around, or zoom in and out, any drawings will stay exactly where they are.
Version 5.1608.2117.0 of Windows Maps is out now, but only for Fast ring Insiders. If you're not an Insider and you have no wish to be, no worries. The updated app with the new features will make its way to the Production ring soon enough.
Thanks to Tony for the tip!