We had a westy and he was very active. They love to run and chase balls, etc. We had a Newfoundland puppy when Max was an adult and Max gave our newf a run for his money. I believe if you can take him to a dog park and let him play with other dogs, that gives the socialization and exercise at the same time. Or if you choose to tether him at least a 30 minute brisk walk a couple times of day.
Westies are very energetic, but all dogs are different, even within the same breed. Generally, a young Westie needs a couple of walks a day, say for 30 minutes, and several play times a day (it's good to have a back yard or nearby park if you own a Westie), but for the older ones simply one walk a day will usually do. Mostly, you need to pay attention to when the Westie seems to be getting overly bored and if it's behavior or temperament changes toward the negative as a result. That is a sure indicator that he/she needs more activity.
The West Highland White Terrier likes to run and play (and dig) outdoors, but must be supervised and inside a secure fence. He is a very energetic little dog who can get much of his exercise from playing with toys indoors.
He can live in an apartment if he is taught early not to bark excessively and if he is taken on a couple of daily walks. An occasional romp in a secure area will satisfy him.