Radar hotspots are not all active
The radar hotspots on the map are not all active at one time. As you move from one to another, you will notice that some are active and not others. If you click on one or two of the active ones, some of those which were inactive previously are now active and some which were active, now are not. It seems that there might be a limit on the number of active hotspots.
Try the link below to see what I mean.