How to make a GPS on the moon? And why that is a practical solution that connects communication and location?

There is no magnetosphere over the moon. That means all communication over the moon's horizon must be made by using satellites. Those communication satellites can use their communication systems to locate the transmitters on the moon. The astronauts and robots who operate on the moon can use laser transmitters that are visible from Earth or photo satellites that can locate them. 

But radio wave-based communication is also suitable, and if those astronauts operate in building sites where is no visual connection with telescopes and satellites. The radio wave-based GPS can be suitable also for locating astronauts and other things on the moon. 

The GPS and communication satellites are the most important technical things on Earth. The GPS and communication satellites can use in the same role on the moon. The GPS is not very hard to make because that system requires four satellites. Six is the minimum if that system covers the poles. In that case four of those satellites are in the stationary positions over the moon's equator. And then two positioning satellites are orbiting the moon by using polar trajectories. 

But if engineers want to provide the non-stop GPS or MPS (Moon positioning system) on the moon's poles they need at least eight satellites if they don't want the satellite communication cuts sometimes. 

In that system, there are four satellites in the stationary equatorial orbiter. And four other satellites are orbiting the moon in oblique polar orbits. The positions of those four satellites must be that two of those satellites see the south and north poles all the time. 

Those satellites can position over certain landmarks on the moon. Those landmarks can be well-known, easy-to-recognize objects like Kopernikus mountain and certain craters. And especially their central hill. 

The surface team can put laser pointers or laser mirrors on those landmarks. And then that GPS (or in this case MPS Moon Positioning Satellites) will position itself by using those laser location systems. Those satellites can have CCD cameras. And they can also locate astronauts and their vehicles by using camera images. 

The satellites can also provide communication services for astronauts on the moon. Communication satellites are necessary tools for moon colonists because the moon has no magnetosphere. And those communication satellites require over-the-horizon communication on the moon.