I tried to link portals, but have no success. I had many failed attempt, but the last one I'll explain. I had the portal key for a LVL4 portal, and I was at another LVL4 portal which was 3km appart, but I couldn't link them. I'm only LVL1 tough, but I'm not sure if that's count or not.
Portals are all around us and can generally be found at monuments, memorials, historic buildings and sites, exterior works of art, significant structures and unique businesses. Portals can be found using the Ingress Intel Map or using your Ingress Scanner. Portals appear white in color if they are uncaptured, green if they have been captured by the Enlightened or blue if they have been captured by the Resistance.
A portal is captured by placing a resonator on a portal. Portals have levels which are determined by their power output. You can increase a portals power output thus increasing its level by upgrading the resonators to higher levels. Keep in mind you can only place resonators up to the level at which you are, e.g. you can place a resonator up to level 4 if your Access Level is 4.
Also, a single player can only place a certain number of resonators of the same level on a single portal. Here is the breakdown:
Level Max # Per Portal
In order to increase your factions total number of mind units, you need to link 3 individual complete portals (portals with 8 resonators) together. Unfortunately, you can not just link any portals together, there are some requirements.
The first requirement, is that you have to have the portal key for the destination portal you wish to link. You can acquire the Portal Key's by hacking both portals. IMPORTANT: The destination portal's Portal Key is consumed by the linking process and without acquiring an extra key by picking one up in the field, you can only get a single portal key for a portal at a time by hacking. So it is important that you rehack the portal to acquire a new portal key after you link it, this will allow you to properly defend your portal.
The two portals being linked need to have enough of a charge on their resonators to sustain the link. This charge level is referred to as the Critical XM health level.
The final requirement is that one of the portals has to have a large enough range to reach the other portal. A portal's level determines its range. The exact formula for a portals range is:
Portal Range = 160m x (average resonator level) ^ 4
Use our mobile friendly portal build calculator to determine what resonators you will need based on the link distance you need to reach. Ingress Portal Build Calculator.
We are unsure on the maximum number of links possible on a given portal, at one time we thought it was 16, but have seen portals with more than 16. As I mentioned above, linking three portals together creates a Control Field and adds to your Factions Mind Units (essentially the teams score). How much of an increase in score is determined by the population covered by the Control Field. E.g. two Control Fields of equal area but one is in rural farm land and the other is in an Urban area, the Urban Control Field will output a higher number of Mind Units.
Due to the cancellation of the penny, I no longer give 2¢ about anything. I may however, give a nickel
My screen usually tells me why -- crosses another link (as Xopher said) or that the target is an enemy portal. When you tap link a portal and the screen tells you to select a key, wait a second and the screen will tell you if there are no linkable portals.