HYG-Database

It might be the hygdata set which can be found here: https://github.com/astronexus/HYG-Database It currently says it has the "Hipparcos-Yale-Gliese" database, with 119,614 stars and the "Tycho-2/Gaia" subset with 118,971 stars. That seems pretty close to the numbers quoted in the demo. I used it previously for a matrix math conversion project translating the NIST JAMA library into a Javascript library. If interested, the test page as a githack link can be found here. Click the "Run 3D Ellipse Fitting on Nearby (100 LY) Stellar Data". My example only uses the 25,000 out to 100 LY. https://rawcdn.githack.com/conceptualGabrielPutnam/JAMA4JS/2...

On the extreme end, if you live in the countryside you can replace GPS entirely using celestial navigation/star tracking. This is commonly used for rockets and satellites but right now if you own a truck or pickup you can easily go completely off-grid by mounting a lens on the rooftop. E.g. http://nova.astrometry.net/ For implementing the system on an embedded device e.g. toy drone, raspberry pi etc., the main data structure you want is a k-d tree together with some sort of evergreen star chart (it doesn't have to be extremely evergreen, current astronomy libraries can easily predict orbits for a couple decades without significant skew/deviation unless you are are aiming for centimeter level geolocation accuracy). For the hardware you can either use existing consumer-grade stuff followed by a ton of image processing with ML as suggested