Those talkgroups are from this system:
Port Of Seattle (P25) Trunking System Profile
www.radioreference.com
That site is Simulcast.
Each of those blue markers represent the location of one of the sites used in the Simulcast. Though radio waves move extremely fast, the transmissions from these various sites receive enough out of sync to cause problems for most scanners. The radios issued to the users of the system are equipped to deal with that, at a cost of multiple times that of consumer grade scanners.
Uniden's SDS series scanners are the only ones currently available that can deal with simulcast, For all the other scanners, it boils down to location & luck. If you are fortunate enough to be at a spot where you are only getting the signals from one tower (the rest being blocked by terrain, buildings, or perhaps something in your residence (metal siding, foil backed insulation in the walls, something large & metallic near your scanner (say a metal file cabinet, or maybe that refrigerator in the kitchen on the other side of the wall).
The Simulcast wiki page, linked above, goes into more detail on the subject, I have seen a couple of threads in this (Whistler) forum of things people have tried. A few of them state that it did help some (for their TRX scanner, but there's no guarantee that any of these suggestions would work well in your area,
