In the ingress intel page, depending on the zoom level, a message on the right-hand side says "Showing L1-L8 Portals. Zoom in to see unclaimed Portals". My question is: is the zoom level in the map dynamically set between locations as to which portals and unclaimed portals to show? Or should the same level always show all claimed portals or all claimed and unclaimed portals?
All portals (including unclaimed) can been seen in zooms 21 - 16 (zoom level 21 is closest in that you can zoom, and zoom level 1 is the furthest you can zoom out).
Zoom 15 shows L1 - L8.
Zooms 14 & 13 show L2 - L8.
Zooms 12 & 11 show L3 - L8.
Zooms 10 & 9 show L4 - L8.
Zooms 8 & 7 show L5 - L8.
Zooms 6 & 5 show L6 - L8.
Zooms 4 & 3 show L7 - L8.
Zooms 2 & 1 show only L8.
When you zoom to level 16 to filter unclaimed portals it will take too much time and effort to discover them because you'll be looking to the map at a very close range. There is a way to show both unclaimed and up to L8 portals at the same time whilst scanning a large area but it creates too much data exchange and loads too much data from a very wide area in every portal level.
Zoom in to zoom level 16 and then zoom out your browser (You can do this by pressing Ctrl and minus in many browsers). This will load portals from every level for a large area. I don't suggest you trying this in a dense area or at least don't zoom out the map too much.