you are correct, but you are opening a quite complex matter here.
You should explain what an SBAS is then, and maybe introduce the concept of GBAS also
To me, and my counterparts SBAS is not a complex matter - SBAS (Satellite-Based Augmentation Systems) is just a means to augment the accuracy of GNSS. To most, GPS is a catch-all descriptor; to me and my peers GNSS is the total of which GPS is one component (GLONASS-K is another component), and the following other systems are other components.
Regarding SBAS, in North America it's WAAS (Wide Area Augmentation System - used in aviation, including the aerial photography you see in Apple/Google/MS Maps; look up the Mr SID TIFF file format and you'll see a file format that I've been using for two decades - an example is each "pixel" is equal to 6 inches, in a vector layer embedded in a Mr. SID TIFF file); in Europe, an SBAS system is EGNOS (European Geostationary Navigation Overlay Service) - and there's other systems around the world; an advantage of SBAS is system uptime and better accuracy.
GBAS is another augmentation system - Ground-Based Augmentation System. This AS runs over VHF, and it's land-based and meant to be accessed by emergency services (often in poor weather conditions) - it works well for both land- and water-based positioning needs. I've needed to access this system - with permission - in areas where access to the clear sky isn't ideal but precision is important, such as on roads in the middle of nowhere. You may not need this type of system on your iPhone but it's a good bet it was used to lay out some of the roads ya'll drive on. And, if you fly, it's a really good bet that the airway landing strip you just landed on utilized this AS to build it out and maintain it...
Another far-more accurate SBAS used here in the US is StarFire, owned and operated by John Deere - it's been around for about 20-odd years. Companies/farmers can lease access to that system - it's pretty much available around the world. You want "accurate"? How about down to about 4 centimeters in a 24-hour lease period?
Download, install, and run the now-free Google Maps Pro. As you mouse over a location you'll see elevations "under" your mouse. Each pixel is tagged with data that was supplied by some sort of AS - Google generally identifies the data source(s) as you move around the interface. A lot of that data was accumulated through aerial photos and survey data purchased from local aggregators (like Metro in the Portland Area and King County in the Seattle Area) - they, in turn, purchased that data from companies I've designed with and surveyed with (and lots of other designers). Years before there was a Google Earth, I used Keyhole - which became Google Earth after Google bought it. Now, there's ties to Trimble (which bought SketchUp) - I use Trimble equipment for my layout work, but that's another long story...
