Left image: residence of Harvard students 6 years after their graduation (1907); made with beads, pins and wires. Middle image: Sources of the 3,000 first letters of appeal sent to Mrs. E. H. Harriman (1912); eight different kinds of pins were used to represent different kinds of appeals. Right image: collection of pins and beads made for maps.
- Willard Cope Brinton (1914) Graphic Methods for Presenting Facts pp. 227-253.
- John Krygier (2010) A Discourse on Map Pins and Pinnage.
- New York Times (1912) 6,000 Letters Beg $267,000,000 of Mrs. E. H. Harriman.