Intel Map (intel.ingress.com) is a website to browse the global Ingress map - not limited by the visual range of the Scanner. The Intel Map can also be used to redeem Passcodes, and is useful for copy-pasting Passcodes on a computer and for iPhone users.
IITC (Ingress Intel Total Conversion, iitc.me) is a set of third-party add-ons for Intel Map that provides additional features on top of the original Intel Map. However, many features require meta-add-ons, and link drawing is not as quick.
While IITC is a modification of official Ingress tools and probably goes against the Terms of Service, there appears to be a silent acceptance by Niantic. Reportedly, following a user campaign in 2014, no agents are known to have been banned due to the use of IITC.