How many polis are there?

Could you please enlighten me on the matter of polis? I'm quite curious to know, how many polis exist in total? Is there a specific count or is it a constantly changing figure? I'm interested in understanding the scope and scale of polis, whether they are numerous or rather rare. Perhaps you could also provide some insight into the nature and significance of polis, if you don't mind. Thank you in advance for your assistance in satisfying my inquiry.