I checked on
outbrain: 8250 widgets
taboola: 7100 widgets
mgid: 3200 widgets
revcontent: 5800 widgets
(I thought widgets means how many websites these platforms have, but it might only mean a subrange of a website, I'm not sure if
I didn't find a way to check how many sites prepellerads and popads have (By the way, zone is just an ad placement on a website, a site might have many zones). But I guess the number is around 1k. (correct me please.)
As for Google Display Network:
Google Display Network (GDN) is a group of more than 2 million websites, videos, and apps where your Google Ads can appear.
As for Youtube Channels:
There are more than 37 million YouTube channels out there.
I'd like to know, if I promote on GDN and Youtube, if it's almost impossible to use blacklist approach? if the tool like theoptimizer.io have almost no effect? What, in general, is the best way to optimize on platforms with huge inventory?
My guess is on these platforms, I should focus more on interesting and demographic targeting, whitelist might be used at the same time, but blacklist are almost impossible unless I spent a huge amount of money.
Thank you guys.
Hello,
just like you said, zone should be just one Ad position and there might be several ones on one site. Same goes for widget, there might be several widgets on one site.
But it's not like this in 100% cases.
Sometimes the publishers install the ad networks codes incorrectly so they might use the same zone code in multiple parts of their website.
With PUSH networks, this get's more complicated since the push lists are usually collected across various websites and these can be mixed into one large list which would be labeled as one placement. On top of that, there is quite a bit of reselling going on in the background, so the same lists can be sold under several IDs in multiple networks... it's quite a mess to be honest 
With POPs, in an ideal case, there is just one POP code on one website so if installed properly, one placement really equals to one site. But again, due to errors and reselling, it might not always be the case.
To put it simply, the system is far from perfect, but we gotta work with what's available 
GDN does offer the option to target specific publishers, you can find the websites that are in your niche and target just those, in case they monetize with adsense.
As far as I know, you can do the same with Youtube and target specific youtube channels so that the ads display just there, at least it used to be that way.
More on YT targeting is here on their FAQ: https://support.google.com/youtube/answer/2454017?hl=en
But again, as you said yourself, with google and youtube it's more about selecting the target group based on demographics and interests/topics and then letting their AI finding similar ones for you, based on what your conversion goals are.