How can I determine the distance between two portals in Ingress? The intel map doesn't have a scale. Figuring out a linking strategy whilst at home is difficult without a scale.
Cole Busby's answer is great information for two portals that are less than 0.5 miles away.
But if you want to know the distance between two portals that are further apart, there is this tool: http://smalltowningress.com/portal-distances.html - it works a bit differently though, in that it shows maximum linking distance based on resonator levels, though the distance is also displayed. First you type in the location of a portal, then you can choose different resonator combinations to see the maximum linking distance and if the destination portal is within distance.
I decided to post this because the heart of your question was linking strategy based on portal distances and this tool should help you answer the question, "can I link these two portals, and if not, what is needed?"
Here's a simple distance calculator.