How do I blend an island outline without overlapping?

[Jack24961193dmvd]

Can anyone help me learn how to use the technique in the photo? When I try doing with the blend tool it ends up overlapping and looking a mess. 

[Monika Gause]

That example probably has been made by Object > Path > Offset path a couple of times.

There are plugins that can create that more easily. But they are not free.

[Scott Falkner]

Try a few itterations of offset path to get the first few outlines around the island to smooth out and eliminate the harbours, bays, and lagoons. Then use the outermost path to blend to a circle.

You’ll have to experiment to find the right balance between offset path (which is always uniform) and blend (which is not). In the example below I used two offset paths then blended from the last path to the circle.