Animating lines on maps is a very common effect. With either Motion version 4 or 5 this can be done very easily, very quickly. These techniques can also be applied to many other situations when doing motion graphics in these apps.
Launch Motion 5, in the Project Browser select the generic 'Motion Project' preset. With Motion 4 simply use File > New Project.
Set the project's total duration in the Project Properties of the Edit menu. Use the start and end navigation buttons in the Transport controls of the toolbar to get the playhead to the start of the project, then Option-Command-I, then to the end and use Option-Command-O to set the playback range to the start and end of the total project duration, if necessary.
Import the map or other graphic element you need to animate a line over. Place it into the default Group, position and size it as needed. If you want to animate the whole map moving along with the animated line, save that until the line is completed. We will look at this once the animated line is completed.
Use the Bezier pen tool to hand draw the line. To use the Bezier tool simply click to make points, and the line will follow the points in the order to create them. To set the last point, either click on the first one to close the shape, or to draw an open shape that doesn't end on the first point, press the Return key. The important things to remember is that the animation follows the order of points you make.
You probably notice at this point the lines form a shape that is filled. Use F4 to access the Shape tab, go to the Style tab, turn off the blue activation button for Fill and turn it on for Outline. Feel free to click and drag the points on your line to move them around and adjust as needed.
Use the Brush Color and Width adjustments for the Outline section to make the line appear as you need it. Then jump to the Geometry tab and adjust the Roundness control to smooth out the sharp corners if desired. Back in the Style tab, set the End Cap to Arrow if you want an arrow head to lead the line along. Finally, it may help to make the line really stand out well by using F1 to reach the Properties tab, and turn on the Drop Shadow section, adjusting as needed.
Use F4 to get back to the Shape tab, in the Outline section, we need to keyframe the Last Point Offset slider to animate the line. With the playhead at the start of the project, click the Keyframe diamond next to First Point Offset to set and adjust to zero. Move the playhead to the next location on the timeline the line should draw to and pause, make a new keyframe, adjust the offset to match. Repeat for every location in the timeline where the line should start and pause its animation. There are three buttons at the top right of the Timeline window, the left one will show keyframe locations in the Timeline. Use this to adjust the timing of your keyframes more precisely.
This step could take up a whole tutorial by itself, but I wanted to give you some tips to help you get started on your own in the meantime: If you want to move everything in the video frame to follow along with the animated line we've created, the easiest method is to keyframe and adjusting the Position and Rotation parameters in the Properties tab of the Group. Do not adjust them for any single layer except for the overall Group both the map and animated bezier line are in. And always remember the 3-step rule to keyframing in Motion:
This is a very quick effect to pull off once you know the very simple process. We're simply using a Bezier line and keyframes. As with all motion graphics projects, think about how much time the animation will need to fill in the original video production it will be a part of. You can use the Write On behavior if desired (a subject for a whole other tutorial), but you have much more control over the animation with keyframes.