This app was mentioned in 6 comments, with an average of 3.67 upvotes
Ekahau Site Survey & Sidekick: https://www.ekahau.com/products/ekahau-site-survey/overview/
You can use your laptop or iPad and get a map of the whole area.
Also, if you want a good mobile app, Aruba Utilities for Android is a solid choice: https://play.google.com/store/apps/details?id=com.arubanetworks.arubautilities
For Android only (IOS doesn't let you grab this info) there is an app in the Play Store called Aruba Utilities. It will tell you what AP you're connected and even let you connect to a specific AP. It will also query the controller to give you more info as well.
https://play.google.com/store/apps/details?id=com.arubanetworks.arubautilities
That is because the Nexus 6 does not support DFS channels, while iPhones, Samsung Phones and Sony Devices do. Check the page here: https://en.wikipedia.org/wiki/List_of_WLAN_channels
In the US, the non-DFS 5ghz channels are 36,40,44,48, 149,153, 157,161,165. Any other channels your N6 will probably not see.
Use the Aruba Utilities App to see what channels your phones can/cannot see https://play.google.com/store/apps/details?id=com.arubanetworks.arubautilities
Aruba Utilities shows the channel width.
https://play.google.com/store/apps/details?id=com.arubanetworks.arubautilities
I wish WiFi Analyzer did.
For android I like Aruba Utilities. Windows (10) I like WinFi and it pairs well with a WLAN Pi if you have one already (I think the main board is no longer being made). I haven't really found a good one for IOS yet but Apple Airport Utility does ok in a pinch. A NetAlly Aircheck G2 is a pretty good investment when budget season comes around.
Aruba Utilities is what i use. same as WiFi analyser, but more functions like iPerf