The .map() operator is one of the most basic operators available, and so it is a perfect candidate to start the example list with.

As we discussed earlier, the first line represents the original Observable and the items on the line are the values that will be emitted by the Observable in the specified order. At the very end of the sequence, there is a termination symbol.

In particular, we are interested in the operation that is being applied here. Let's take a look at the following diagram:

The following block represents the .map() operation being applied:

It says that the elements are transformed by changing the form of a circle into a diamond. So, the circle elements that were received from the original Observable will become diamonds in a new Observable.