Roaming is a wireless telecommunication term mostly used with mobile devices. It refers to a mobile phone being used outside the range of its native network and connecting to another available cell network. In simple terms when actively using data roaming, you basically leave one BSSID and authenticate/associate to a new BSSID.
Even though there is no dedicated feature in NetSpot to survey the roaming signal, you can enable Active Scanning specifically for connected networks, while performing a survey in NetSpot. This way you will be able to clearly see which Access Point (BSSID) you were connected to in each sampling point of your survey.
This approach will help you analyze the “roaming” signal according to your technical definition of roaming as it relates to _your_ network configuration.