When viewing your list of populations on the populations page, you'll see a "Status" column for every one of your populations. This will either read "Up to Date" or "Updating". We'll even tell you how long ago your data was updated, so you know you're always seeing the most up-to-date information. 

Your population will say "Updating" when the population is processing, which either means it's a regularly scheduled update (per your data source's sync frequency which is set on your data source), or you made a change to your population (including just creating it).