The Rediscovered Map Collection of the John Hay Library offers vivid examples of mapmaking and map use in the United States from 1800 to 1920. This collection testifies to the changing technology and diversifying demands that made maps more available throughout this epoch. Libraries often have hidden treasures of this material, uncataloged and unknown to the community. With some organization and commitment, Americana paper maps can be arranged into a vibrant collection. We break down this epoch into 30-year periods to analyze the tremendous changes that occurred and how they impact libraries today. [ABSTRACT FROM AUTHOR]