I wanted to see how much Islam has spread into the Middle East and Europe over the last 100 years. The Association for Religion Data Archives just added a terrific dataset that has a lot of historical data regarding the world’s religious demography. The title is: U.S. Religion Census: Religious Congregations and Membership Study, 2010. A complete description of the coding can be found here.
In addition, there’s an animated gif of the progression of Islam from 1900-2010 available here.