There are a few things out there that I find really cool, and Illustrators ability to create multiple strokes on one path is one of those cool things. This infographic in one line and that is it, no shapes. Check this one out, it is simple and just awesome. And it will also show you how to create a dotted line in Illustrator, an odd feature that many people don't know about!
Start with a path, add a stoke to it.
Open up the Appearance Panel, you'll need this to add strokes to strokes. May seem odd, but this is how it is done.
In the lower left of the Appearance Panel, click on the Add New Stroke button.
This shows how one stroke can be on top of another stroke.
Click on the Stroke Link in the Appearance Panel. Click on the Dashed Line Box and set the dash length to 0. Yes ZERO. Why Zero? Then nothing shows up, right? so turn on the Cap options with the rounded end. This gives you two "half circle" caps that make a dot. And with a Zero stroke, it looks like a dot.
Setting the gap on the dashed line gives you the spacing between the dots.
Click on the last stroke and click on the Appearance Panel cheese grater and choose Duplicate Item, this gives you a copy of the stroke and its attributes.
With the duplicated stroke, make it a different color and set the stroke weight to be smaller than the stroke below it.
You can also move each stroke above or below each other, just like you would a layer.
Here is the stroke on top of a stroke on top of a stroke. And this is all one path! Not separate circles on the path.
To save this effect, go under the Window Menu and choose Graphic Library. Select the path with the multiple strokes and drag it into the Graphic Styles Panel and it will add the style to panel for future use.
Now any shape you create you can quickly add the newly created stroke style to any shape that has a path.
Adjust the stroke of the paths to change the look of the dots.