I am interested in your usage of LoRaWan.
I am trying to figure out how to use LoRaWan sensors - applications from project view.
I have 2 temperature sensors in 2 different rooms and now send this to an application “environment”
But if I want to monitor 2 different houses? How about your houses but also clients? How would I monitor a city?
All temperature sensors on one Application, other type of senors in a second application and then combine these 2 applications in a web server?
Whatever you are doing with LoRaWAN will require some kind of processing and presentation layers. TTN does not provide this, the console allows access to some data but no features like graphing, correlation etc. That is where you need to choose to create something yourself or use one of the existing integrations like cayenne mydevices. Depending on the integration you use they provide different capabilities.
For quick proof of concept and for workshops I usually pick cayenne as its quick and easy to get a basic dashboard for free. For next steps or if more processing is required for a customer either a customer specific solution is implemented on customer resources or they’ll be integrated into our multi tenant dashboard solution.
The use of one or multiple applications depends on data format, nodes used and what needs to be achieved.
As for clients:
If you’re going to sell devices, for which you won’t know how clients will use them, your only choice is OTAA, with a unique AppEUI for each device. If a single client wants to use multiple devices, then multiple AppEUIs can be added to a single Application, if that’s what they want.
If you’re going to sell services (which come with a device, which should only be used for that service) then you could use a single AppEUI (and hence: single Application) for all devices, and within your service implement your own authentication mechanism to ensure clients can only see devices linked to some account.
But even then it will be much nicer to allow buyers to use the device any way they like. So again a unique AppEUI per device (or a way to reprogram the device) would be best. The ttnctl command line interface or the Application Manager API can be used to easily register many AppEUIs to a single application.
Slightly related: How to best write an application that contains many nodes with different measure data types.
My question was more in regard to TTN applications.
Lets say that I have with self built temperature nodes.
So I create an application: MyName_Temperature_Home.
Later I want to add new temperature nodes to the home om my GF.
So I create a new application: MyGF_Temperature_Home
Now do we get the first problem, I cannot easily take one Temperature node to my GF without programming.
So it is tempting to create on generic application: Generic_Temperature_Nodes and feed all nodes I create to that single application.
This may work well if I only have 10-20 nodes, but what happens when I bow have 1000 nodes if I start to create a business out of it?
Now some newer nodes may now also be able to transmit humidity.
So payload of a device may contain a type byte that explains what type the data is
So how do you scale this well to the future when you add new types and different of nodes, start with nodes across cities, and may reach 1000,10.000 or even higher mixed with
I am just curious how other people would build large scale projects that exceeds hobbyist territory 
My previous answer still applies…
What you do in TTN depends on your nodes. For some nodes, for instance your own nodes, you would be able to create a payload and decoder that works in a way where you could combine the nodes in one application and have your dashboard/processing back-end handle the differences in payload.
For other nodes you might not be able to change the payload and creating decoders for the different payloads might be a challenge. That calls for different applications one for each for different node type.
If you are going to create/resell nodes and want to offer a service based on them the best solution is probably to register them all on one application (for the same type) and provide access to the data in your own service.
At least that is the solution we’re using for larger deployments.
Can 1 application process large amounts of nodes? Is there a limit?
An application on TTN does not ‘process’ nodes. It is a container for the nodes, the integrations and payload functions.
I am not aware of any limits.
I appear to have holes in my knowledge about TTN. Since I am all new, this may sound logical
I may misunderstand what “application” means in the TTN context. It seems not to be the same as in “windows application”.
Right now learning about MQTT
Please check my post about using cayenne lpp format with IOTFactory.eu may be useful.