map reading
TRANSCRIPT
MAP READING
Prepared by:
Joffrey Estrada
What Is a Map?
A map is a representation of a geographic area, usually a portion of the earth’s surface. It may be shown in many different ways, from a traditional map printed on paper to a digital map built pixel by pixel on the screen of a computer.
Maps can show almost anything, from the electric supply grid of your community to the terrain of the Himalayas to the depths of the ocean floor. A map can be practical, directing travelers from one point to another through confusing terrain, or explaining the world by attaching specific types of information to geography. But maps can also entertain and invite exploration.
Maps can be drawn in many different styles, each showing different faces of the same subject and allowing us to visualize the world in a convenient, informative, or stimulating way. To use maps effectively, just learn the few simple skills described here. In addition, be aware of these important facts:
(1) No map is perfect. People make maps from data they collect with certain tools. Even computer-generated maps depend on programs designed by people and on data collected by human-designed machines. People make mistakes and machines are never totally accurate all the time, nor can any device record every detail of a landscape. Therefore, maps can contain errors and inaccuracies. Because of data errors or cartographic errors, a certain village may not be exactly where the map shows it or a mountain peak may not be exactly as high as it appears on the map.
(2) Maps grow old. The world is constantly changing both physically and culturally, so maps can become outdated, no longer showing the world accurately. Modern technology has provided a partial solution—computers have made it possible to renew maps easily without redrawing them. However, appropriate information reflecting changes in the world must still be collected periodically and used to revise the maps’ databases.
(3) Maps are biased. Because maps generally do not show every single feature of a chosen geographic area—every tree, house, and road—the cartographer must decide the projection and scale for the map and decide how much detail to present. The purpose of the map as well as the cultural background of the cartographer often dictates this process, called generalization. Information on the map and how it may be distorted can influence what people think about the world and what they do.
Map Types The first question to ask about a map is what its theme
is. The theme is the particular aspect of the world that the map attempts to show, such as roads, borders, vegetation, or statistical data. Maps can be divided by theme into three categories.
1. General maps, are those that contain many themes and give a broad picture. General maps are often practical, showing the world in a way that allows people to get from one point to another without getting lost, or allows them to learn about the overall layout of an unfamiliar place without having to go there. An example of a general map is a road map of a country showing major cities, mountains, rivers, landmarks, etc.
2. Thematic maps, which contain one or a few themes and show in-depth information. Thematic maps can show almost any kind of information that varies from place to place, such as a country’s population or income level by state, province, or county, with each division colored differently to indicate the relative level of population or income.
3. Charts, which are accurate maps of routes of travel used for ocean and air navigation. They must be updated frequently so that captains and pilots know of current dangers along their route.
Forms of Maps
1. Ancient Maps. The first maps made by people were probably lines drawn in sand or small pebbles and sticks arranged on the ground.
2. Modern maps are published for the long-term use of many people. Printed maps are the simplest forms.
Printed Maps a. Flat maps, are the simplest forms. They show
the world as flat—that is, in two dimensions. On a printed map, relief—mountains, valleys, and other terrain—is shown with special symbols to make up for the lack of depth.
b. Relief maps, are rigid flat maps with actual bumps and depressions added to indicate elevated landforms and low areas—that is, in three dimensions. They are usually made of clay or molded plastic, and the relief is usually exaggerated to give a greater impression of depth.
c. Stereograms. In between the effects created by flat maps and relief maps is the visual experience created by stereograms, which are flat maps or aerial photographs positioned in slightly differing pairs. Viewed through special 3-D lenses that fool the eyes, stereograms give the effect of viewing actual relief. Globes are spherical models of the Earth, the Moon, and other planets. They give a more realistic impression of features on a curved surface.
3. Computer Maps, are the most versatile. A mapping program can dynamically show many different views of the same subject, allow changes in scale, and incorporate animation, pictures, sound, and Internet links to sources of supplementary information. A person can update a computer-generated map with new information by simply supplementing the map’s database, allowing the map to grow over time to present more geographic detail and more themes. Having a powerful digital map is like having dozens of printed thematic maps overlaid on a particular area, each electronically connected to an immense library of information on the main theme and on many related ones.
How To Use a Map How people use a map depends on the type of map
they have and what sort of information they want from it. A. Simple maps, only one or two types of information may
be available and few or no map skills are required to use it. For example, a sketch of a neighborhood may only show what relationship a particular house has to the street corner or whether it is farther from there to the market or to the school.
B. Complex maps can indicate actual distance, the exact location of many important land features, elevation, vegetation, political divisions, and many other aspects of the world. To interpret such a complex map, some basic map skills are required…
Map Elements Most maps, including the majority of
maps of the earth, share a number of basic features. They assume a certain projection and scale, they usually express location in terms of coordinates, and they have a legend.
Projection The way the geography of the earth is taken from
the globe and reassembled on a flat surface is called the map’s projection. Another way of thinking of projection is this: Every point on the globe can be projected by a straight line onto a transparent form wrapped around the globe. The shape of the form and how the points are spread onto it determine the type of projection.
Some common forms are cylinders, cones, ellipses, and flat planes, giving rise to cylindrical, conic, elliptical, and orthographic projections. There are many types of projection, each distorting the spherical surface of the earth in a different way and each with its practical advantages and disadvantages.
Scale The size of a map in relation to the earth is its scale, which is
usually stated as a fraction or ratio. The numerator, at the top of the fraction, is one unit on the map and the denominator, at the bottom of the fraction, is the number of the same units that are represented in the real world. For example, a scale of 1/10,000 means that one centimeter on the map is equivalent to 10,000 centimeters on the ground. As a ratio, this scale would be shown as 1:10,000. The larger the denominator and the smaller the fraction, the more of the earth is represented on a single map. Therefore, small-scale maps show a large piece of the earth, and large-scale maps show a relatively small piece. Another way to think of map scale is that items in small-scale maps appear small, whereas the same items in large-scale maps appear large.
Computer maps may have a varying scale that changes according to the “zoom” level of the view. The more zoomed in, or closer you are to the earth, the larger the depicted scale.
Coordinate Position The surface of the globe is divided into a spherical grid
for the convenience of finding certain points. The grid consists of imaginary lines called latitude and longitude.
A. Latitude is a series of concentric circles paralleling the Equator and extending to both poles. B. Longitude is a series of meridians, or longitudinal lines drawn between the poles at regular intervals
that pass perpendicularly through the Equator. Where a particular latitude crosses a particular
longitude, a pair of numbers, or coordinates, can be assigned. Every point on the earth has a set of coordinates that indicate its position relative to every other point.
Latitude is measured from zero at the Equator to 90 degrees north and south at the poles. Longitude is measured from zero to 180 degrees west and east. The reference lines for counting are the Equator, for latitude, and a line drawn through Greenwich in England, the prime meridian, for longitude. These are the zero lines.
A degree of latitude is equivalent to about 112
kilometers (about 70 miles). Because longitudinal lines converge toward the poles, degrees of longitude vary according to the position on the earth. At the equator, one degree of longitude is the same length as one degree of latitude, and at the north and south poles, the distance between degrees of longitude is zero.
Degrees are divided into 60 minutes, and each minute is divided into 60 seconds. For example, the Eiffel Tower in Paris has the following coordinates: latitude 48° 51' 32' north and longitude 2° 17' 35' east. Sometimes, coordinates are expressed in decimal minutes instead of minutes and seconds, so the coordinates of the Eiffel Tower can also be written as 48° 51.5333 north latitude and 2° 17.5833 east longitude.
Some maps have other special-purpose coordinate systems, such as the State Plane Coordinate System used on maps in the United States or the Universal Trans-Mercator (UTM) system used on many military maps.
Legend Maps use sets of symbols to indicate the
placement of real objects. The legend is a block of text or a window in which the symbols used on the map are explained.
Legend symbols can include icons to represent buildings, different colors to indicate elevation, different types of lines to indicate borders or roads of varying size, and dots and circles to show the relative population of towns and cities. If the details of a map look unfamiliar, take a moment to study the legend before proceeding further.
Direction: Which Way Is Up? Most maps give a reference point to indicate how a
direction on the map corresponds to a direction in the real world. This is crucial when using the map to travel between points. A good map indicates a cardinal direction for such orientation, usually by an arrow pointing north.
Maps from past centuries used various cardinal directions. Some older European maps placed East at the top, pointing to the area then known as the Orient, leading to the term orientation. Old Muslim maps put South facing upward.
Modern maps usually adopt the convention that the top of the map corresponds to North, the bottom to South, the left edge to West, and the right edge to East.
The poles representing the rotational axis of the earth do not correspond to the magnetic poles, the direction a compass points. This is because the magnetic poles constantly change position or wander. The north-pointing arrow on many accurate maps is divided into two parts, one indicating polar and one indicating magnetic north.
The angular difference between these is known as the map’s magnetic declination. For example, according to a 1987 map of Moscow, the compass points to magnetic north at 7° 46' to the right of true polar north, so the magnetic declination according to this map is 7° 46' east. The declination changes with location on the globe and it also changes with time as the magnetic poles wander. Some localities have a change in magnetic declination of several minutes per year. Lines of longitude are oriented toward the rotational axis of the earth. Digital maps are made in reference to this axis and usually ignore magnetic north.
The Ups and Downs of Maps: Elevation
Topography adds a third dimension to the flat-map picture of the world. Cartographers use different techniques to indicate topography, which means the hills and valleys of the surface of the earth. Early maps used bars, or lines of overlapping triangles to show hills or mountain ranges. A few ancient maps, including a Buddhist map from 14th century Japan, show mountains as artistic, three-dimensional figures. Symbols such as hatched or spoked symbols were also used on some European maps. Modern maps show mountains in shaded relief, called hill shading. Traditional topographic maps use concentric lines, called hypsographic lines, to indicate elevation. Each line is assigned a height above sea level. Corresponding lines indicating ocean depth are called hydrographic lines.
Instead of concentric lines, color maps often use a standardized color scale to indicate elevation: Sea level is blue, low land elevations are shades of green, higher elevations range from tan to brown, and the highest peaks are shown in white, suggesting snow. Deeper shades of blue correspond to deeper parts of lakes or oceans.
Relief Map Relief maps are three-dimensional models of the terrain in an area; on them, color and scale are used to indicate geographical features rather than simply to delineate political boundaries. Because of this feature, relief maps are extensively used in engineering and the military. This map shows portions of Alaska and northwestern Canada.
Drawing a Cross-Section The map on top is a topographical map. The map’s curving lines, or contours, are labeled with numbers indicating how high above sea level the contours are. The second map is a cross-section of the map on top. The x-axis (the horizontal axis) of the cross-section corresponds to the line from A to B on the topographical map. The y-axis (the vertical axis) of the cross-section is used with the x-axis to plot the height of each contour where it crosses the A-B line. This creates a series of dots; by connecting the dots, a cross-section of the landscape is created.
Weather Map
Topographic Map In addition to showing general locations and political boundaries, topographic maps depict the geology and special features of an area. This type of map offers many advantages. For instance, most backpackers use topographic maps to navigate through wilderness, planning their routes with obstacles and landmarks in mind. If they should get lost, they can find their bearings again by aligning their map and compass to a prominent feature observed nearby. A key on each map indicates the distance scales and special symbols (for features such as railroads, schools, airstrips and water towers) used to create it. Generally, the green on a topographic map indicates forest or vegetation, while the white areas indicate areas that are bare of growth. Series of brown lines indicate mountains and hills, showing elevation and relative steepness. Each line represents a specific unit of elevation; where the lines are very close together, the terrain is quite steep.
Map Legend A legend is an explanatory list that defines symbols appearing in a map or chart. Some symbols, such as the mountain range and waterfall symbols shown here, may resemble the features they represent.
Scale The scale of a map defines the relationship between distance on the map and the corresponding distance on the earth. (Left,) The units of measurement shown in the scale represent 1000 mi, top, or 1000 km, bottom, on the earth. (Center,) One unit on the map equals a distance of 10,000,000 units on the earth. (Right,) One unit on the map equals a distance of 1,000,000 units on the earth.
Magnetic Compass A free-spinning magnetized needle points toward magnetic north on a compass dial. Magnetic north is located in a different place than the geographic North Pole, or true north. The location of magnetic north is determined by the orientation of the earth’s magnetic field. The location of the North Pole is determined by the axis of the earth’s daily rotation. On maps and navigational charts, true north is offset from magnetic north. To find true north a correction, called the magnetic declination, must be made on all compass readings.
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Earth’s magnetic field is believed to be generated by charged particles that circulate in the Earth’s liquid outer core, along with forces caused by its rotation. An electric current is generated, which in turn creates a magnetic field. The magnetic field protects the Earth by deflecting high-energy particles from the Sun. Without it, life on Earth would be impossible. The magnetic field weakens and reverses itself every few hundred thousand years as part of a natural cycle. When magnetic reversals occur, there may be a period when a magnetic field is absent, which may cause difficulties for animals that rely on it for navigation.
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Marine Chart and Plotting Tools Marine navigators use charts and plotting tools to measure distances and to record a ship’s progress as it travels through the water. This marine chart displays water depth and geographical features of a segment of the northeast coastline of the United States. Dividers, center, help the navigator measure distances on the chart. Parallel rulers, right, are used to transfer compass bearings from the compass rose, a diagram of a compass on the chart, to other parts of the chart. The navigator lays the parallel rulers over the compass rose, visible here through the transparent rulers, then walks the rulers, one leg at a time, across the chart and records the desired compass bearing on another section of the chart.
Taking a Bearing In navigation, the direction of one object from another is called a bearing. To take a bearing between a ship and an island, a navigator would measure the horizontal angle of the island clockwise from north. Bearings are commonly measured in degrees, as shown here.
GPS Receiver with Map A Global Positioning System (GPS) receiver links with an array of satellites to give users their location. Many GPS units have enough memory capacity to store maps so that users can pinpoint their map location and use it to plot routes to their next destination.
GPS Satellite A total of 24 U.S. Global Positioning System (GPS) satellites orbit overhead and provide accurate positioning and navigation information for both military and civilian use. Solar cells power each satellite and its atomic clocks. Antennas on a satellite continuously transmit timing information from the clocks. The signals can be picked up and processed by a GPS receiver to determine exact location and altitude.
GIS Image A Geographic Information System (GIS) is a computer system that synthesizes, analyzes, and displays many different types of geographic data in an understandable form.
The GIS-generated image seen here shows the locations, represented by black dots, of industries releasing toxic chemicals in Los Angeles County. This image has been superimposed on census tracts—color-coded according to the distribution and size of different racial or ethnic groups in the area—from the United States Bureau of the Census. The green areas are inhabited mostly by Asians, the blue areas by blacks, the purple areas by Hispanics, and the yellow areas by non-Hispanic whites. The image was produced as part of a study carried out at the University of California in Santa Barbara to examine the relationships between pollution, race, and residential patterns. The image illustrates how a GIS can combine and clearly display many kinds of information for a given geographic area.
Ptolemy’s Map of the World This map shows the world as Greek geographer and astronomer Ptolemy envisioned it in the 2nd century AD. Ptolemy’s map, based on the accounts of sailors, traders, and armies who had traveled in Europe, Africa, and Asia, shows the Indian Ocean as an enclosed body of water. This misconception persisted in Europe until 1488, when Bartolomeu Dias rounded the Cape of Good Hope in southern Africa and sailed from the Atlantic Ocean to the Indian Ocean.