I've explored Ingress in two places: Manhattan and rural New Hampshire. At least for leveling purposes, it was trivial to walk around Manhattan and interact with portals. How might one find portals in a less dense part of the world? At the moment, I'm limited to dragging the Ingress Intel Map around likely areas, but this is pretty inefficient and requires I zoom very far in to see unclaimed portals.
First off you can always zoom to that area on the intel map and ask in faction chat - local players can tell you the best spots.
Otherwise, my best bets for higher portal density in rural areas are: - Main Streets (and nearby 'downtown' areas) - Colleges - Parks and public gardens - Larger Cemetaries with elaborate tombstones - Larger Churches with multiple buildings
These are things you can usually pick out on Google Maps and then lookup on Intel.
For unclaimed portals in 1s and 2s use Google Maps to find Churches, Post Offices, and Libaries. Those are either going to have portals or be good for you to submit.
You could always drive around and see what pops up on the scanner too.