VLANs and VPNs

While reading my notes, I have come across few diagrams with firewalls with VPN which allow remote access to the network. My understanding of VPNs are that a user would essentially get a LAN IP Address allowing user access to other network services.

1) However in no point of the notes did it mention whether the IP Address would have to be limitted to the VLAN of the firewall.

2) Notes also did not mention why a VPN server (which usually is the firewall for some reason, which I am not yet certain why), is usually right up top of a network diagram. Could I have my VPN server (firewall) sitting deep within the network? What implications would that bring?.

Thanks!