Hey! I really liked Ian's way, but I was thinking of the following:
Population (Sierra Leone) * % of people who have access to the internet (Given that Sierra Leone is a developing country, we can say roughly 15%) * % of people who are interested in social media (age is a key factor here, so expect a high penetration rate within the younger age brackets and the opposite for the older age brackets) * average number of selfies per person per week.
Would be great to hear some feedback on this approach.