How does purchasing tiles affect cultural border expansion?

As far as I know, borders can grow when a certain amount of culture is accumulated in that city.

But how does purchasing tiles affect this cultural accumulation? Do the accumulated culture become nullified and start over or are they kept and carried over to the next new tile?

Solution 1:

I was able to test this myself and confirm that a few Reddit threads, including this one, match my observations.

If you buy a tile, it does not reset the culture progress towards acquiring a new tile. However, it does increase the amount of culture required to claim the next tile, but all progress is retained.

Comment from the thread:

It doesn't reset growth.

However, if you're at, say, 50/60 culture needed to expand, and you'll expand, in, let's say 2 turns, and you buy a tile... any tile... suddenly you're at 50/120 culture to expand, and you'll not expand for 14 turns.