I find the easiest way to find the right “place” to use for filtering, is to go to an observation that is definitely inside the area you want, and then under the pin location map in the observation view you can select “details” and drop down a list of places that encompass that specific location. In this example, on the left are the system places, and on the right are the ones the community creates. Countries will usually be on the left. Clicking on the place takes you to the observations for the place.
What I particularly like, is it sometimes shows user created places that you may find useful, such as the “Waiapu Ecological District” in this case, an area that I will find very useful in future now that I have seen it exists!