I always use this graph when I’m teaching Lesson 9 (“The Task Remaining”) of Perspectives.
 
World A B C Percenages, Changes, 1900-2050
It shows the world’s global population, divided up as percentages, for each year from 1900 through 2050 (2025 and 2050 are projections).
This is based on the data from the Center for the Study of Global Christianity, as presented in the Status of Global Mission (which you can download at http://www.globalchristianity.org). 1925 and 1950 are interpolated from data in the World Christian Encyclopedia and World Christian Trends (two earlier works). 1975 is assumed from 1970; the percentages are essentially the same even though the populations are different.
The red area represents the percentage of the world that is unevangelized. The gold area represents Christians of all traditions. The green area represents those evangelized non-Christians: those who have access to the Gospel but have chosen against it (or not yet for it).
While the church is adding people every year, what this graph shows us is that the percentage of the world that is Christian has been essentially stagnant for the last century. There was significant process made in making the Gospel available between 1900 and 2000 (especially in the period from 1975 to 2000), but this rate has now trailed off.
Part of the reason for this is that we have “picked all the easy fruit”: a lot of the newly evangelized from 1900-2000 were ethnoreligionists. Another reason for the slackening off is that all the people who surged into the lower half of the red zone in the 1900s to 1920s are now in the ‘green zone’ thanks to their work, and a lot of people are going to the ‘green zone’ because there’s still work to be done.
The reality is, 90% of all Christian work (pastoral, evangelistic, missionary or otherwise) happens among people that are already at least nominally Christian. About 9% of work happens in the Green Zone. Less than 1% of existing ministry activity happens in the red zone. Thankfully there has been a large reorientation of cross-cultural missionary workers, so I doubt those %s hold true amongst the cross-cultural force per se, but nevertheless the unevangelized world is still growing (although the % of the world that is unevangelized is declining slightly, the absolute numbers of unevangelized individuals is growing, by about 52,000 per day).
We need more intentional going to the unevangelized, “red” zone!
Feel free to use this graph in your own Perspectives teaching…