What is the “ping pong” effect mentioned here?

Question

I was reading this post on the official forums.

It says

If you, like me, like to shape your maps then make sure you have them all in the same area as you want to put your elder in that area in order to utalize [sic] the ping pong effect between shaper and elder influenced maps.

What is this "ping pong" effect? How can I profit/benefit from it?

When answering, please note:

• I have not shaped any map under the "War for the Atlas" system, last season I did not play much, if not at all.
• I play standard, league requires too much time for me.
• I have not yet completed The Hidden Architect quest

Answer 1

When you complete a Shaper-influenced map that is adjacent to an Elder-influenced map, the map you completed will usually flip from Shaper to Elder influence instead of returning to its default status. The converse is also true -- an Elder-influenced map will usually flip to Shaper influence on completion if it's adjacent to another Shaper-influenced map. This is the "ping-pong" effect that the post is referring to.

Shaper- and Elder-influenced maps have added monster packs and can drop Elder/Shaper rare items. These items can be quite valuable, as they can have mods which are not available on other rare items.