Mapping the Chesapeake: Cartography in the 1600s

Navigational technology in the 1600s was nowhere near as precise as today’s GPS technology. However, it was good enough to get sailors from one place to another and produce somewhat accurate maps. Smith’s map is remarkably accurate for a map from the time and is easily recognizable as the Chesapeake Bay. In order to create the map, he would have taken hundreds of measurements throughout his voyages and recorded them in a logbook. He used a variety of maritime tools to take measurements.

Quadrant, circa 1650

Peter Ifland Collection, The Mariners' Museum

A QUADRANT is a device used to determine latitude. Latitude lines are imaginary lines that run horizontally across the Earth. Your latitude tells you how far north or south of the equator you are. To measure latitude with a quadrant, the sailor holds the device to their eye and aligns it with the horizon. They then adjust the slider to measure the angle between the horizon and the sun. This had to be done at noon when the sun was at its highest point in the sky.

This type of sundial is known as a "diptych" sundial due to the pair of folding ivory panels.

Jamestown-Yorktown Foundation Collection

But how did sailors know what time it was before clocks were invented? To tell the time, Smith would have used a SUNDIAL. Primary sources from the time tell us that Smith had an ivory sundial that doubled as a COMPASS.

A sundial tells the time by employing a string, or "gnomon," that casts a shadow when held up to the sun. The compass is used to align the sundial to a North-South orientation. The shadow cast by the string points to a marking on the sundial indicating the time. A compass is a tool that tells which direction is north. A magnetized, freely spinning magnet inside the compass always points towards the magnetic north pole.

Unfortunately, the sundials that the Jamestown colonists brought from Europe were designed to be used at a different latitude, and therefore would not have been very accurate at telling the time! John Smith still would have been able to use his sundial to measure regular increments of time, which is what he needed in order to produce accurate measurements.

National Maritime Museum, Greenwich, London

A CHIP LOG was a tool used to measure a ship’s speed. The “log” was a spool that held a long rope with knots tied in it at regular intervals. The “chip” was a triangular piece of wood or metal tied to the end of the rope.

Every thirty minutes, a sailor would throw the chip overboard into the water. He would let the rope unspool for thirty seconds and count the number of knots that unwound. If five knots passed, he was traveling at five nautical miles per hour. This helped the ship’s navigator figure out how far the ship had traveled.

Penobscot Maritime Museum

Sailors took measurements of speed and direction every thirty minutes. To record that information, they used a TRAVERSE BOARD. The traverse board was simply a wooden board with pegs.

The top part was a compass rose with 32 directions and eight holes extending outwards. A peg was placed in each of the eight holes, starting in the center, every thirty minutes to chart the ship's direction.

Similarly, the four rows of pegs on the bottom of the traverse board were used to record speed. The rows, split down the middle, represented thirty minutes of time for a total of four hours. The columns represented knots, the nautical measure of speed.

At the end of the four-hour watch, the pegs were removed and the next watch started over again.

How Accurate Were Smith's Measurements?

Right image
Credit: NASA

Just how accurate was John Smith's map of the Chesapeake Bay? Compare it to a satellite image to find out!