Are there portals that do not appear on the intel map?

The Intel Map displays portals in the Ingress game. Are there undiscovered portals that do not appear in this map?

I know that new portals are added from time to time. What I want to know is if there are existing portals that I can find by exploring with the game running.

Edit 2013-01-15: I am aware that it is necessary to zoom way in on the Intel map to see low-level and unclaimed portals. I am specifically wondering if there are portals that do not appear on the map at any zoom level because they have never been visited/discovered.

I ask because the portals on the Intel Map have notes like, "Discovery: Khayman 01/14/2013". Are these the names of players who have discovered previously hidden portals - or are these the players who submitted geotagged pictures to get portals added? I am skeptical of the latter possibility because some of the portals in questions are post offices and libraries and do not have pictures.

Every portal appear in the intel map, at the correct zoom level.

To see unclaimed portals (grey ones), you'll have to zoom very close.

As said by Matthias Urlichs, to see a biggest region, zoom out with your navigator : Ctrl -

The 'Discovery' label is a misnomer, it indicates the first player to capture the portal when it was last neutral. For eg., say you blow up all resonators on an enemy portal - when you place the first resonator to claim it, the portal will now say 'Discovery: Jesse' (w/e is in-game nick).

As already mentioned by others, the Intel map does show all unclaimed portals provided the zoom level is high enough.