Selecting just the outlines of a set of geometry?

[archz2]

How can I select just the outermost lines of a collection and thicken them? Just by click, click, carefully picking the outer lines is a very tedious process. 

There must be a smart and fast way. 

I downloaded the following file from the website pimpmydrawing.com. 

 

It has a very neat set of thick outlines and thin inner lines. 

I would like to do the same for the following file. 

 

american-football-player-celebrating-sanaa-people-105-pimpmydrawing.ai geometry set1.ai

[MEB]

Hi @archz2,
Welcome to Affinity Forums
There's no automated way to pick just the outlines since they are all separate segments and all have the same attributes as the inner lines.