In our sermon discussion group, the idea of a world map where each country / continent’s size was based on Christian population was brought up. The closest I know of is found in The New Context of World Mission by Bryant L. Myers.
The photo below is from the 1996 edition. A 2003 edition is available at the above link. This is a terrific resource with plenty of excellent graphics / stats.
Perhaps someday Worldmapper will have such data.
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