May be it is a basic knowledge but I need to clarify

What is a nest? Is there anyone in western Sydney? How do you recognize a nest on your phone? Is it like a pokestop?

It can be anything from a group of 2 or 3 spawns, all the way up to a very large park or area.

Nests are identified by having specific spawn points that change to something else every couple of weeks.

If you play PoGo, then you have most likely been to a nest - but you just didn't realise it.

https://thesilphroad.com/atlas

It can be only less than 100 square meters, or bigger than 1 square kilometer.

Nests can range from a huge area (like the Berlin mega-nest) to a single spawn point. This means that some nests cover a very small area and thus are difficult to identify.

When trying to identify a nest, keep in mind that participating spawn points will spawn the nesting species only 25% of the time. So don't expect to walk into a nest and be immediately surrounded by a hoard of the nesting species