How would I change this sentence to active form?Saratoga Springs, New York, has been called the gateway to the Adirondacks.
In order to change this sentence into the active voice, the subject must perform the action in the sentence, which is not the case in this sentence. There really is no way for the subject -- Saratoga Springs, New York -- to perform an action, therefore a different subject must be added in order to create the active voice. Here is the sentence written in active form:
Many people have called Saratoga Springs, New York the gateway to the Adirondacks.
Now, your subject (people) is performing an action (have called) and the sentence is now in the active voice.