Summary of the
maps for a variety of purposes. A map can be defined
as a graphical abstraction of the real world. Most
maps describe both cultural and physical features
found on the Earth's surface in two-dimensions. Maps
can be of two general types: reference maps and thematic
maps. An example of a reference type map is the topographic
map. This type of map focuses on providing location
based information. Thematic maps usually display
the spatial distribution of one geographical phenomenon
or the geographical relationship that occur between
two or more phenomena.
a number of techniques in the process of map creation.
A number of mathematical transformations can be employed
to best depict the three-dimensional surface of the
Earth on a flat map. However, these transformations
do create some type of distortion artifact. Distortion
is usually manifested in the following geographic
properties: distance, area, shape, straight line
direction, and the bearing of cardinal direction
from locations on the Earth. Some map projections
have the ability to minimize the distortion of some
of these properties. For example, using the Mercator
projection drawn angles on a map's surface are true.
It is extremely
difficult to draw maps true to life. For this reason,
maps are normally drawn at a reduced scale. Map scale
can be expressed as the ratio between map and actual
ground distance. On most maps, the scale is described
as representative fraction. Scale can also be described
as a verbal statement or a graphic illustration.
Finding locations on maps is usually
done with a coordinate system. The two most common
systems found on maps are Geographical Coordinate System
and the Universal Transverse Mercator System. The Geographic
Coordinate System places a three-dimensional grid system
over the Earth's surface and locations are determined
relative to two coordinates: latitude and longitude.
Measurements of latitude determine location in a north-south
direction relative to a point at the center of the
Earth's polar axis. Longitude measures the west-east
position of points on the Earth's surface relative
to a circular arc called the Prime Meridian.
The Universal Transverse Mercator System
uses a two-dimensional grid for find location of the
Earth's surface. It is also based on the Transverse
Mercator map projection. This system is more complicated
than Geographic Coordinates as location is determined
relative to 60 - six degree longitude wide zones that
Distance can be difficult to measure
on maps because of the distortions produced by map
projections. However, if the map has a scale larger
than 1:125,000 these distortions are insignificant.
When measuring distance one must be aware of the map's
scale especially if these measurements are being used
in the real world.
Direction on maps and the real world
can be measured relative to true, grid, or magnetic
north. On maps, the easiest way to measure direction
is relative to the lines produced by the Universal
Transverse Mercator System. These grid lines are aligned
relative to grid north. Finally, compass direction
can described either by using the azimuth or the bearing
One useful field instrument for determining
location on the Earth's surface under field conditions
is a GPS. A GPS uses triangulation and a network of
satellites to calculate location to an accuracy of
less than 30 meters.
Humans use the position of the Sun to
determine time relative to a 24-hour day. Because of
the Earth's shape and its rotation on a central axis
time varies from location to location. To make time
keeping simple, a system has been developed that uses
24 times zones to standardize the keeping of time.
This system was suggested by the Canadian Sir Sanford
Fleming in 1878. Fleming's system has undergone a number
of modifications since it was first proposed. The current
system, called Coordinated Universal Time (UTC), became
the standard legal reference of time for the world
in 1972. UTC is determined from six atomic clocks and
this time is then applied relative to the 24 time zones
found on our planet.
Topographic maps are detailed two-dimensional
representations of the natural and human world. These
maps are used for a number of activities. One important
feature found on topographic maps is that the Earth's
vertical surface is depicted by using contour lines.
Topographic maps also used an advanced system of symbols
to describe the features found on the Earth's surface.
The online lecture describes many of these symbols.
A contour line is an isoline that connects
all points on the Earth's surface that have the same
elevation. On topographic maps, contour lines are drawn
at a uniform vertical distance known as the contour
interval. Many maps also use index contours. The interval
used on a particular maps depends on the amount of
A topographic profile is a two-dimensional
diagram that represents a vertical cross-section lifted
from a topographic map. These diagrams provide a simple
way of visualizing relief in a particular region of
Remote sensing is any process that collects
data about an object from a remote location. Geographers
use a number of mechanical devices to achieve this
process. These devices contain advanced sensors that
can capture information via the reflection or emission
of radiation from objects. Devices used for remote
sensing are constructed to sense certain wavelength
bands. The objects that are sensed have particular
spectral signatures and one has to match the object
to the sensor. The simplest and most common device
employed by Geographers to carry out remote sensing
is aerial photographs.
In the 1960s, the deployment of high
altitude satellite caused a revolution in remote sensing.
Many orbiting objects were outfitted with sensors to
complete specific remote sensing jobs. Remote sensing
of the Earth's climate for weather forecasting began
with the launching of a number of satellites called
TIROS. Over time sensors became more sophisticated
and some of them were used to monitor the Earth's surface
for a number of applications outside of weather forecasting
(LANDSAT, SPOT, and RADARSAT).
Recognizing objects from a remotely sensed
image is often a difficult process. Many objects are
hard to identify because their appearance in the image
is unfamiliar to our memories. We see objects in our
environment mainly from a oblique perspective. Objects
that are remotely sensed are often imaged from above
and the sensors used in the imaging process may be
recording electromagnetic signatures that are outside
human vision. To aid in object recognition users often
use a methodical process that identifies features based
on shape, image tone or color, pattern, shadow, and
Geographic Information Systems (GIS)
are another important tool used by Geographers. These
systems combine computer cartography with database
management software. GIS is used to: a) measure natural
and human phenomena and processes from a spatial perspective;
b) store these measurements in digital form used a
computer database and digital maps; c) analyze collected
measurements to produce new data or discover relationships;
and d) Depict the measured or analyzed data in some
type of display.
List of Key Terms
Remote Sensing, Aerial
Photography, Atmosphere, Attribute, Azimuth,
Earthquake, Easting, Electromagnetic
Energy, Element, Equator,
Projection, Geocoding, Geographical
Coordinate System, Geostationary Orbit, Global
Positioning System, GOES, Graphic
Mean Time, Grid
Contour, Infrared, International
Date Line, Isoline,
Landsat, Latitude, Lithosphere, Longitude,
Projection, Meridian, Microwave
Grid Reference System, Miller
Cylindrical Projection, Mollweide
Magnetic Pole, North
Aerial Photograph, Opisometer, Orthographic Projection, Origin, Ozone,
Remote Sensing, Polar
Radarsat, Radiation, Rectangular
Coordinate System, Reference
Map, Reflection, Relationship, Remote
Method, Sea-Level, Sinusoidal
Equal-Area Projection, South
Magnetic Pole, South
Pole, SPOT, System,
Mapper, TIROS, Topographic
States Geological Survey, Universal
Transverse Mercator, Universal
Transverse Mercator Grid
Problems and Exercises
(1). What is a map?
What two basic forms do they come in? How are projection
systems used to portray the Earth's surface on
a map? What problems are associated with projecting
the Earth's surface on a two-dimensional map?
(2). Describe how the geographical
coordinate system references the location of features
found on the Earth's surface.
(3). Describe how the Universal Transverse
Mercator grid system references the location of features
found on the Earth's surface.
(4). Discuss the relationship between
map scale and map distance.What techniques are commonly
used to measure distance on maps?
(5). Describe the various ways direction
is measured on a map. How are directions measured
in the real world with a compass used on a map? How
do the azimuth and bearing system differ in depicting
(6). How was the measurement of time
standardized for the world?
(7). What is a topographic map? How
does it use maps symbols to represent natural and
human constructed features found in the environment?
Why are contour lines found on this type of map and
how are they used?
(8). What is remote sensing? What types
of remote sensors have been developed to monitor
the Earth? Describe some of the guiding principles
of object identification that are used for feature
(9). What is a GIS? What
type of activities are carried out on these computerized
systems? Describe the difference between element
and attribute data.