Cartography concept

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A Student's Guide to Mapmaking-by Ralph Ehrenberg

What Is a Map?

Step 1: Where Are We?

Maps are one of the most important types ofdocuments associated with exploration. A map is agraphic representation that facilitates a spatialunderstanding of things, concepts, conditions,processes or events in the human world. They areused by explorers to help find their way. They are

also prepared by explorers to document or recordwhat in fact they discovered.

There are many types of maps, each determined bythe purpose for which it is designed. The roadmaps that your parents use are way-finding orroute maps that guide them from one place toanother. The daily weather charts that you see ontelevision are special-purpose maps of naturalphenomena that help people plan whether or notthey will travel to a particular place! Thegeographical maps in your textbooks show thedistribution of various things or processes overlarge areas. What types of maps do you thinkexplorers used and prepared?

The first step an explorer takes in preparing a map is to determine his or her location. Thelocation of any point or place on the earth's surface can be understood only with reference to itsdistance and direction from another point or place. The easiest way to do this is to use familiar

Page 1 of 7Lewis and Clark : Cartography

12/29/2005http://www.edgate.com/lewisandclark/cartography.html


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Step 2: Determining Projection and Scale

landmarks.

Your bus driver useslandmarks everyday as he orshe drives you safely to

school. You may observe theselandmarks or guide points aswell. They may be in the formof man-made objectsrepresenting the human orcultural landscape such astheaters, churches, andsynagogues. They may betopographic or physicallandforms such as rivers andhills. Or they may beprominent plants such as largetrees and distinctive shrubs.Such landmarks provide arelative location or mentalframe of reference, and areuseful for guiding people oversmall areas.

Explorers and mapmakers, however, must determine the exact location of a place or point onthe earth's surface so that whoever uses their maps can easily find any site depicted withoutdepending upon another person for guidance.

This is done by dividing the earth's surface into a grid system of imaginary lines similar to theway a football field is marked off to help officials and spectators locate the placement of thefootball with precision and accuracy. When applied to the earth's surface, these lines aredesignated parallels of latitude and meridians of longitude.

Latitude establishes position north or south of the equator while longitude determines positioneast or west of a prime meridian, the zero point from which longitude is measured. This iscalled the geographic coordinate system of parallels and meridians, and provides a scientificframe of reference for locating any place on the earth's surface. More information on latitude,longitude and prime meridian can be found at the following Web pages:

- Comptons Encylopedia; Longitude and Latitude

- Hammond Wac; Longitude and Latitude

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Step 3: Adding Symbols

The transfer of this imaginary grid system of parallels and meridians of the Earth ( a sphere) toa small, flat map, however, cannot be done without distorting in some way the map's shape,area, distance or direction and changing its scale. These distortions can be easily observed bydrawing a grid system of parallel lines on a large grapefruit and then laying the peeling flat.

To compensate for these distortions, mapmakers construct map projections to emphasize or de-

emphasize one or more of the basic map properties cited. Follow this link to view different mapprojections and their properties:

- Map Projections

Map scale refers to the proportional relationship between the distance of two points on a mapwith the actual distance on the ground. Map scale can be expressed in words ("one inch equalsone mile"), graphically (with a bar divided into sections), or as a representative fraction(1:24,000 or 1/24,000). The larger the map scale, the smaller the area shown. The followingWeb page illustrates map scale:

- Map Scale

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Once the map's projection and scale aredetermined, the next step undertaken by anexplorer is to add features of the physical,natural, and cultural landscapes that will mostaccurately and vividly represent the pattern and

texture of the area mapped. This is done bysimplifying (generalizing) the features to beshown by using symbols.

Map symbols are small graphic images that standfor something else. They may be depicted bypictorial images, abstract combinations of pointsand lines, or tonal shading and color tints. Forexample, an explorer might show an Indianvillage by using a miniature picture of a teepee.

The mapmaker often uses a key or legend toindicate what symbol matches what feature. Forexamples of map symbols used in orienteering,visit this Web page:

- Map Symbols

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Step 4: Naming Things

Mapmaking in the Time of Lewis and Clark

Compass Route Mapping

The final step in the preparation of an explorer's map is selecting andapplying geographical names that identify relevant features,landmarks, and places.

Geographical names are fundamental elements of maps. They alsoprovide important reference frameworks in our daily life.

During the early history of America, explorers and mapmakers named many of our mountains,rivers, and towns. Today, these names form part of our cultural heritage and provide clues tothe history of our country's settlement and people. A list of almost two million physical andcultural geographical features in the United States is available through the following link:

- Geographical Features

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Two hundred years ago when Lewis and Clark set out to explore the Far West, the basicprinciples and techniques of scientific mapmaking were well established. As early as the secondcentury A. D. the Greek geographer Claudius Ptolemy prepared instructions for the constructionof maps using latitude and longitude as a geographical frame of reference. During the great ageof European seagoing exploration, Portuguese, Spanish, Italian, Dutch and English navigatorsdeveloped and improved a variety of instruments to measure one's position on the Earth'ssurface.

By 1800 overland explorers relied primarily uponcompass route mapping to prepare their maps. This isalso called "dead reckoning." In compass route mappingor "dead reckoning," mapping is based upon determiningdirection and distance along the line of exploration. Thedirection or course of the route is determined bymagnetic compass, an ancient instrument invented in

China and used in Europe since at least the eleventhcentury.

By the beginning of the nineteenth century, mapmakers were aware that their compassespointed to the magnetic north pole rather than the geographic north pole, and that they had tomake corrections for this variation. Several magnetic variation maps of North America had




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Celestial Navigation

Map Publishing in 1800

been published by 1804 to help surveyors make these corrections but none existed for the FarWest.

z Distance was determined by a variety of methods. These included devices that measuredthe speed of travel:

z In rivers or streams they used log-lines or counted paddle-strokes.z

On land they counted their steps (pacing), and later, used viameters (odometers) attachedto a wheel.z For more accurate measurements, some explorers also carried a one-hundred link chain

called a Gunter's chain. This chain measured precisely 66 feet in length.z The height of the mountains and hills along the route were often measured as well, using

an instrument called a barometer.

Nineteenth century explorers checked the accuracy of their compass bearings by celestialobservation. This is called celestial navigation.

In the Northern Hemisphere, latitude was determined by measuring the altitude or angle of theNorth Star, Polaris, from the horizon, with finely scaled brass instruments calledoctants orsextants. Determining the altitude ofPolaris on land required another instrument called anartificial horizon since the true horizon is generally obscured.

Longitude was more difficult to determine during a cross-country expedition. The mostaccurate method is to compare the time of a portable clock orchronometerset according to a

prime meridian with local time determined by celestial observation. The results were thencalculated by reference to astronomical tables of transits (ephemeris) by experts known ascomputers. Unfortunately, the marine chronometers of the period were too bulky and sensitiveto carry overland and pocket chronometers were often too fragile to survive long distances.

Local time in North America was determined by measuring lunar distances (the distancesbetween the moon and certain stars) and calculated according toNautical Almanac andNautical Ephemeris, first published in England in 1765.

Upon completion of an exploring expedition, the field maps would be redrawn on one sheet at asmaller scale and then turned over to an engraver for publishing.

Today, we are surrounded by maps. We see them daily on television, in our newspapers, in ourbooks, and on our computer screens.

But in 1800, maps were rare, expensive, and available only to the leaders of society. They alsolooked different than the maps we use today. In 1800 maps were printed from either wood




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blocks or engraved copperplates and they were hand colored. These were time-consumingprocesses that required skilled craftsmen and artists. For an illustrated description of woodcutand copperplate engraving, see the following link:

- Woodcut and copperplate engraving

The detail shown on a map was also morelimited in 1800 than today. Large areas ofmaps were often left blank for lack ofinformation, or they were filled in withdecorative lettering or fanciful pictures. Ifterrain features such as hills and mountainswere depicted, they were generally shown inthe form of "hairy caterpillars" or simpledrawings of hill forms. These techniques werewell adapted to both woodcut and copperengraving.

Maps also reflected the lack of accurate,detailed field surveys available to mapmakers.Since no standards existed to guidemapmakers, symbols and lettering variedgreatly from map to map.

The selection of the prime meridian alsovaried from place to place before theadoption of Greenwich, England in 1874.Often it was measured from the nation'scapital or from the city in which the map waspublished. In the United States, mappublishers often used Washington, D.C., asthe prime meridian during the first half of the

nineteenth century.

Most of the maps available in the UnitedStates at this time were published in Englandor France. Because the United States had fewtrained mapmakers in 1800, many of the firstAmerican cartographers were recruited fromEurope or were former military officers.




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