There aretwo types of mapping in BizTalk for message transformation.
- One-To-One Mapping
- Many-To-One Mapping
One-To-One Mapping: this is most commonly used. In this there is one source schema & one destination schema. Below is the sample picture for the same. This map can be applied in Orchestration, receive & send ports.
In this map you need to add source & destination schema and apply link in between them. Also, you can use functoid for data manipulation.

Many to One Mapping: This mapping can only apply in orchestration. There will be multiple Input message and one output in this mapping, and it is not applicable for receive port or send port.
- Create all the message types you need (all the input messages and the output message)
- Create an orchestration.
- Drag a construct message shape and a transform shape onto there.
- Configure the transform shape and add all your input messages to the Transform Source list

- Set the output message as usual and click OK
- A map file should appear in your project. Open it
- You will see on the left-hand side all you input messages are now available in the mapper (under Root/InputMessagePart_1, _2, etc)

Now you can start linking source to destination in mapping.