Michael Tierney shows a quick and easy way to get automated proximity using an expression in Ae.

Have you ever wanted shapes to react to some others in After Effects automatically? You can do that with a simple expression. This tutorial from Michael Tierney shows a fast and easy way using an After Effects expression that Breton Brander created. 

The tutorial covers how to adjust the scale of shapes using expressions based on the proximity of other ones in the scene.

On a related note, this tutorial from Creative Dojo’s VinhSon Nguyen also shows something similar, triggering an attribute change when elements reach proximity to each other.