I'm David Thorson. I'm a guide at Monticello. Thomas Jefferson's father was Peter Jefferson. He was a surveyor, a map maker, and a justice of the peace in Colonial Virginia. In the late 1740s, Peter Jefferson and Joshua Fry together surveyed the colony of Virginia and in 1751 published a map of their surveys, which became the standard reference map of Virginia for almost 50 years.

Thomas Jefferson was just eight years old when that map was published, and he developed a fascination with maps, globes, and atlases, became a surveyor like his father, also developed a fascination with what Jefferson later termed to be the mysterious west. Shadwell, where Jefferson is born, it's the edge of the west in 1743. This is almost the limit of British Colonial expansion into North America.

Fifty years later, Jefferson becomes the President of the United States and changes the map of the United States and the destiny of the United States forever with the purchase of the Louisiana Territory in 1803 that not only doubles the size of the country, it pushes the entire nation—not only its physical boundaries—but its vision of what it's going to become to the west. And so from the map of Colonial Virginia of 1751 to the map created after the Lewis and Clark Expedition, 1804 to 1806, the United States has now become a transcontinental power, what Jefferson envisioned as an "empire of liberty."