It's all good and well being able to tell where you are, but it's a different story giving someone directions to get to where you are, or where you need to go.
For this, I think a system similar to the Halo game's directional bearing would be best. In Halo, directions would be given out as direction "upspin" and "downspin" based on the ring's movement, with a metric value. You would often hear their characters say "We need to get XX clicks upspin" etc. So Yliakum would have that measurement, but unlike Halo, it would need to be measured in degrees rather than kilometres.
As the other directional value would be distance from the point at which you are directly beneath the Crystal, I would assume.
However, that is not the only way of approaching it. N,S,W,E is still valid as the planet Yliakum is inside would still have an electromagnetic polarity field like any other planet, and as such measurements could always be done that way, allowing for more accurate, grid-based mapping and directions.