2. 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.
3. 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.
4. (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physically and culturally, so maps can become outdated,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.
5. 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.
6. 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.
7. 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.
8. 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.
9. 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.
10. 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.
11. 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…
12. 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.
13. 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.
14. 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.
15. 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.
16. 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.
17. 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.
18. 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.
19. 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.
20. 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.
21. 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.
22. 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.
23. 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.
29. 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.
30. 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.
31. 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.
32. 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.
33. Earth’s magnetic field is believed
to be generated by charged particles
that circulate in the Earth’s liquid
Earth’s magnetic field
outer core, along with forces caused
by its rotation. An electric current is
generated, which in turn creates a
magnetic field. The magnetic field
23º
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.
34. 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.
35. 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.
36. 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.
37. 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.
38. 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.
39. 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.
