Cartography and Maps for Beginners
A map is an image that shows where places or landmarks are located in relation to other places and landmarks. Explorers use maps to help them get from one place to another. Explorers may also make maps in order to keep a record of what they have found. Not all maps are used for the same purpose. Some maps are designed to show the user a route or path. Others may show weather systems, or they may show distributions of animals, plants, or other things over a particular area. Which of these maps do you think explorers would use?
Step One: Determining Location
When an explorer begins to make a map, he first determines his own location. The locations of places and points on the earth are only understood by looking at their direction or distance from another place. The simplest way to understand these relationships is by using recognizable landmarks.
For example, school bus drivers follow landmarks each day when he or she transports students to and from school. You probably notice these landmarks too. A landmark may be a man-made object, such as a church or theater. It may also be a physical landmark, such as a hill or river. Landmarks provide us with a frame of reference so that we can figure out where we are located in relation to other familiar places.
Though most of us use landmarks only to determine where we are, mapmakers must know exactly where they are on the surface of the earth so that they can make a map that any person can use. Mapmakers create these maps by dividing the surface of the earth into a pattern of imaginary lines. These lines form a grid of meridians of longitude and parallels of latitude.
Longitude determines whether a place is west or east of the prime meridian, while latitude determines whether the point is south or north of the equator. This system can be used to determine the exact location of any point on the Earth.
Step Two: Determining Scale and Projection
When mapmakers try to transfer the latitude/longitude grid onto a flat paper, they cannot do it without distorting the directions, distance, area, or shape of the map in some way. You can easily demonstrate this distortion by drawing a grid pattern on a grapefruit, peeling it, and flattening the peel. To address the distortions, mapmakers develop different map projections that emphasize a basic property of the map.
Step Three: Adding Symbols
After determining the projection of the map and its scale, mapmakers add physical and cultural features to the map to represent the texture and pattern of each area depicted. Mapmakers accomplish this by creating a system of symbols that represent different features. A map symbol is a small image that represents a specific place or thing. Symbols may be pictures, letters, or abstract drawings. Mapmakers typically include a legend with the map, which is a box that explains the meaning of each symbol used.
Step Four: Naming Things
A mapmaker's final step involves selecting names for places, landmarks, and features on the map. During early American history, mapmakers and explorers were responsible for giving names to towns, rivers, and mountains. Many of these names are still used today and have become part of our cultural heritage. They provide information about the history of our country and its people.
Mapmaking in the Time of Lewis and Clark
Lewis and Clark began exploring the Far West two hundred years ago. By this time, the techniques and principles used in mapmaking were well-developed. In fact, Claudius Ptolemy, a Greek geographer, had already prepared instructions for creating maps using the ideas of longitude and latitude. During the era of European sea exploration, English, Dutch, Italian, Spanish, and Portuguese navigators invented and improved many different instruments that could be used to determine positions on the Earth.
Compass Route Mapping
Compass route mapping, or dead reckoning, was the main method used by mapmakers by 1800. Under this method, mapping involves determining directions and distances along a specific line of exploration. To determine the course, mapmakers use a magnetic compass, which is an instrument that points magnetic north from any location on the planet.
Explorers did not learn that magnetic compasses were pointing to magnetic north until the early 1800s. Before that, they thought the compass pointed to the geographic North Pole, which is in a different location. Corrections had to be made for this mistake. By 1804, several maps of North America were published to make the necessary corrections.
Mapmakers determined distance using a variety of methods, including devices that measured travel speeds:
- On land, mapmakers counted steps or used odometers attached to wheels.
- To measure the height of hills or mountains, mapmakers used a barometer.
- For streams and rivers, they counted paddle strokes and used log lines.
- Some mapmakers used a 66-foot chain to gain more accurate measurements.
Explorers in the 19th century used celestial observation to check compasses for accuracy in a process known as celestial navigation. To determine latitude in the Northern Hemisphere, explorers used brass instruments to measure the angle or altitude of Polaris, the North Star. These instruments were called sextants or octants. When explorers were on land, they also needed an artificial horizon to determine the altitude of the North Star because the actual horizon was usually obscured.
It was more difficult to determine longitude. To determine longitude most accurately, explorers used chronometers, which were portable clocks, set using celestial observation. They calculated the results using ephemeris, which were astronomical tables. However, these chronometers could only be used on water because they were too heavy to carry on land and did not travel well.
To measure the local time in North America, mapmakers measured the distance between certain stars and the moon. They used these measurements to calculate the time with a 1765 book entitled Nautical Almanac and Nautical Ephemeris.
Map Publishing in 1800
After an explorer completed his expedition, he would redraw field maps using a smaller scale. He would then give them to an engraver. In today's world, we see maps everywhere. They are on computer screens, in books, and in newspapers. However, maps were rare in the 1800s. They were expensive, and only leaders of society could usually obtain them. They were very different from maps today. Most of these older maps were engraved on copper plates or printed on wooden blocks. They were also colored by hand. The process of creating a map was lengthy and required the skills of artists and craftsmen.
In 1800, maps showed much less detail than they do today. Maps of large areas often included a lot of blank space where information was unknown. To fill in the space, publishers sometimes drew fancy pictures or decorative letters. When maps included mountains or hills, the drawings were simple. At this time, there were no standards for the symbols mapmakers used, so they varied considerably from one map to another.
Before the prime meridian's official adoption in 1874, mapmakers selected a line to be the prime meridian on their own. Most mapmakers used their city or the nation's capital. In fact, many United States maps used Washington, D.C. until 1850. The United States didn't have many mapmakers during this time, so most maps available in the country came from France or England.
One of the most prominent mapmakers in the U.S. was George Washington, our first president. He surveyed lands and mapped out large portions of the frontier. Another important mapmaker was Thomas Jefferson, our third president. The maps Jefferson and Washington prepared are some of the best examples of what mapmaking was like at the end of the 18th century.
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