You can have nice autocomplete in hangouts that returns name and picture when you give it incomplete email. It also returns so called google id, which links all of your data. Instead of running this set of weird scripts you can open hangouts in browser, click "New Converstation" and start typing emails, then look in dev tools.

Then it just opens https://www.google.com/maps/contrib/+person id and there are your reviews on google map with locations obviously.

Then it tries to fetch your public albums from google photos using same technique, but that does not work anymore. When it did work, it extracted meta info from public albums. That's pretty much it.

Looks like Google has a mostly internal user id ("gaia_id"), once you've got this small identifier you can look on each Google related site for publicly available information relating to that user id.

Looks like Google is aware of it as the reference to gaia_id has been removed from Youtube pages source (Aug 2020), locked down public accessibility of photo albums (Sep 2020), and prevented connected email address leaks from Webmaster tools (Sep 2020).