I think Equestria can be used to describe both the region and the continent, as well as the governing body within it, similar to the United States of America, sometimes just called "America", even though "America" is the name of the two continents, one South, the other North.
So Equestria the Region/Continent reaches from the frozen north down to the badlands, but Equestria the government extends only as far as the crystal empire, which I believe to be a sort of "offspring state" like a colony that has their own government but still has respect for their "parent nation" like… Canada, I guess. Like how they still have the queen on their money or whatever.
This is only modern Crystal Empire, though, Crystal Empire under Sombra was more like Nor-, I mean Only Korea. about the Crysal Empire before Sombra, I don't remember what canon lore says. But today's CE is run by Heartbutt, appointed by Sunbutt.
Other areas of the continent of Equestria outside or beyond the Governing Body of Equestrias control are places like the Badlands, and Everfree Forest. Though the fact that the ruins of Castle of the Two Sisters lay in the Everfree Forest implies that this was not always the case, or, at least that the forest has expanded since they lived there together.
An aside: I was expecting the mane 6 to turn the castle of the two sister into a clubhouse of sorts, since the first few episodes of that season were focused to tidying it up and such, but nooooooo we got Alicorn Princess Twilight's Crystal Treehouse Castle Playset
Anyway. Let's take another look at what sort of government Equestria has. The entire region is under the care and responsibility of two princesses, but Ponyville (and we can assume that other towns, too) have a Mayor. We might assume this is an elected position, but it seems that mayors are more or less local administrators, with little more to do besides make sure their towns run smoothly.
This brings up a question I hadn't thought of. Now that Twilight is a princess, and resides in Ponyville, in her own Stupid looking
castle, how does that affect the power dynamic there if at all?