It is generally understood that all islands fly across the same paths over the world at speeds varying based on the individual island's mass and always following the same path - the same orbit.
That said, because of the varying speeds and the sheer number of islands, it means that some slower island will very rarely cross the paths of other islands - it could be weeks, months, or years before they come anywhere close. But they never collide (this probably happened at some point in the past, but doesn't seem to anymore).
But in order to plan for resource gathering, trade or even travel, it is important that Geonomers map the orbits of other islands that come close to their own.
Geonomers - with the helps of Cloud Skim Pilots - plant markers on passing islands to make them easier to recognize and track. It is not always required, if the islands have distinctive features. The Geonomers will not the time, date, relative position and speed of the island sightings and share their data with other members of the Fellowship of Geonomers.
They have agreed on a marker convention, and will compare their data to establish and confirm the orbital patterns of other islands. For most major islands, the data is very robust and widely propagated among Geonomers, serving as the basis of their experiments.