i want to add widget to monitor how many devices by location

Hello! The first idea that comes to mind is to use Groups. You can organize devices by, for example, location and have them grouped accordingly. Or, you can group them by any of the examples you've cited in your post by making them Custom Properties. Groups can also use dynamic queries based on Custom Properties to add new devices to a group.

For example, let's say your group is based on a location Custom Property. When you add a new node and designate the location custom property as part of adding the node, the dynamic query will pick that up and automatically put the device in the correct group.

I would suggest you consider making all these fields custom properties so you can track that information and also consider using it in other areas of the Platform in the future. Then decide which one you'd like to group the devices by. I think you may have the most success using location as the grouping property. 

You can then use the Groups Summary classic view (My Dashboards - Home - Groups) to monitor your groups and status. You can copy that view, like any of the other classic views, and customize it as you wish. You can also report and alert based on groups 

I think this may be an efficient way to organize your nodes and give you additional features, such as alerting, you can utilize beyond just modifying the Tree Widget. 

Additionally, you can use any of those custom properties as Account Limitations to customize the user experience. For example, you can have dashboards customized for the users in each location so they focus on the devices they're responsible for and do not have to sift through anything else. This would be platform-wide, so the experience would apply to views, alerts, reports, and any other features. I'm not sure if that is also something you'd be interested in, but I find that customizing and optimizing your users' experiences is a valuable tool for a lot of customers. 

I hope this helps! If you have access to the customer portal and are not familiar with Custom Properties, Groups, and Account Limitations, I'd suggest checking out the recorded Platform training: Customizing Views, Maps, and Accounts. Also, perhaps signing up for Office Hours with a Platform trainer in your time zone to further answer questions and assist you.

So first off, everything cheryl1 said is solid advice. And her training is always worth every minute you spend there. 

I find that we have to track the devices that are routers manually (same hardware used in for both in some cases, so I have a custom property for it. Below is a sample of SWQL that I might use to get the counts you want. I filter out stuff I don't want for my environment, but you will want to look at your data (maybe in SWQL studio from the SDK) to tailor it to what you want to see. I did use 2 custom properties, the first for location. You might be using the location field on the node populated by SNMP, here that doesn't play nice across all devices, so we track it in the custom property. Then there's the router property I already mentioned, which isn't a string, we used a yes/no data type. 

SELECT N.CustomProperties.LocationName, 
Case -- I used a case statement to take my yes/no custom property and convert it into a human readable category
    When N.CustomProperties.Router = 1 Then 'Router'
    When N.CustomProperties.Router = 0 Then 'Switch'
End as [Network Device Type]
, Count(N.NodeID) as [Devices]
FROM Orion.Nodes N 
Where N.Category = 1 -- Fitler so only network devices display
and Not N.Vendor like 'Avaya%' -- these devices are network that aren't router/switch so I added filters
and Not N.Vendor like 'Check%'
and Not N.Vendor like 'Citrix%'
and N.CustomProperties.LocationName is not Null -- This filters out locations that haven't been set. 
Group By N.CustomProperties.LocationName, N.CustomProperties.Router

Oh! Look at that! jm_sysadmin that's a great solution too! That's the beauty of THWACK it's a community and we can all share, and learn from each other's ideas. And thank you for your kind comments

hi all

noted thank you 

hi all

noted thank you