Understanding Hiera settings and like it's working

Hello, I've recently found a structure of puppet ready and functional using hiera, but I don't know like it's working. my hiera settings: /etc/puppetlabs/code/hiera.yaml

:backends:
  - yaml
:yaml:
  :datadir: "/etc/puppetlabs/code/environments/%{environment}/hieradata"
:hierarchy:
  - "hostname/%{city}/%{trusted.certname}"
  - "profiles/%{::location}/%{::service}/%{::profileserver}"
  - "profiles/%{::location}/default"
  - "city/%{city}"
  - "virtual_%{is_virtual}/%{virtual}"
  - "os/%{kernel}/%{osfamily}"
  - "os/%{kernel}/default"

#:merge_behavior: deeper

/etc/puppetlabs/code/environments/production/manifests/site.pp

$city          = define_server($trusted['certname'],'city')
$location      = define_server($trusted['certname'],'location')
$service       = define_server($trusted['certname'],'service')
$profileserver = define_server($trusted['certname'],'profile')

an example of settings in hiera hierarchy /etc/puppetlabs/code/environments/production/hieradata/profiles/aa/puppetmaster/master.yaml

---
######################################
#####     puppet-agent             ###
######################################
puppet_agent::master: true
puppet_agent::vardir: '/opt/puppetlabs/server/data/puppetserver'
#puppet_agent::logdir: '/var/log/puppetlabs/puppetserver'
puppet_agent::rundir: '/var/run/puppetlabs/puppetserver'
puppet_agent::pidfile: '/var/run/puppetlabs/puppetserver/puppetserver.pid'
puppet_agent::codedir: '/etc/puppetlabs/code'
puppet_agent::storeconfigs: true
puppet_agent::storeconfigs_backend: 'puppetdb'
puppet_agent::reports: 'puppetdb'

The question is, how the puppet knows what are the profiles, services and cities of the servers? I've already looked on facts of the agents but don't found this variable! thanks.