The spotty (polka-dot pattern) visualization could be a result of combination of several factors:
- too many channels are being monitored with a single adapter;
- the adapter has some hardware problems;
- the speed of walking as well;
What can be done to avoid such results:
- Walk slower: the slower you walk, the more beacon frames from various AO you get captured per each meter of your path.
- Make your scanning cycle shorter: turn off unnecessary (unused) channels.
- Use several identical USB adapters. Two or three adapters will split the job and capture more data at the same time from different channels.
- Take additional surveys: add some walks either continuous or point-to-point in the same area, especially at critical locations.