Summary of the Chapter

Geographers use 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.

Cartographers use 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 run north-south.

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 systems.

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 relief depicted.

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 the landscape.

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 texture.

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

Active Remote Sensing, Aerial Photography, Atmosphere, Attribute, Azimuth,

Bearing, Biosphere,

Cartography, Contour Interval, Contour Line, Coordinated Universal Time,

Earthquake, Easting, Electromagnetic Energy, Element, Equator,

False Origin,

Gall-Peters Projection, Geocoding, Geographical Coordinate System, Geostationary Orbit, Global Positioning System, GOES, Graphic Scale, Greenwich Mean Time, Grid North, Grid System,

Hydrosphere,

Index Contour, Infrared, International Date Line, Isoline,

Landsat, Latitude, Lithosphere, Longitude,

Map, Map Projection, Map Scale, Mercator Projection, Meridian, Microwave Radiation, Mid-Latitude Cyclone, Mid-Oceanic Ridge, Military Grid Reference System, Miller Cylindrical Projection, Mollweide Projection, Multispectral Scanner,

Northing, North Magnetic Pole, North Pole,

Oblique Aerial Photograph, Opisometer, Orthographic Projection, Origin, Ozone,

Parallels, Passive Remote Sensing, Polar Axis, Prime Meridian,

Radarsat, Radiation, Rectangular Coordinate System, Reference Map, Reflection, Relationship, Remote Sensing, Remote Sensor, Representative Fraction, Robinson Projection, Rotation,

Scientific Method, Sea-Level, Sinusoidal Equal-Area Projection, South Magnetic Pole, South Pole, SPOT, System,

Thematic Map, Thematic Mapper, TIROS, Topographic Map, Topographic Profile, True North, True South,

United States Geological Survey, Universal Transverse Mercator, Universal Transverse Mercator Grid System,

Vertical Aerial Photograph,

Weather Map,

 

Study Questions, Problems and Exercises

Essay Questions

(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 direction?

(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 recognition.

(9). What is a GIS? What type of activities are carried out on these computerized systems? Describe the difference between element and attribute data.