Finding rare resources like oil can be hard sometimes. Scrolling over the map to
(a) figure out where an island with that resource might be unlocked or
(b) finding the resource again that you unlocked earlier, but now need for the first time
can be a little frustrating.

I had unlocked an island with oil some time ago and now need it for the first time and had a hard time finding it, surrounded by all kinds of other buildings.
Also I was wondering if there is a second island that offers oil. I was not sure if there is none or if I just missed it while looking around.

Ideas that might help:
(1) add a counter somewhere that shows how many of a resource type are on the map like: Oil 1/2 (one unlocked, two available total)
(2) some mechanism to "jump" to all resource locations (like find idle worker in some RTS games)
(3) add some kind of a minimap that shows rare resource locations as well