2.3: Modeling Earth’s Surface Fall Semester 2015

Objective  Discuss the advantages and disadvantages of using a globe.  Describe what information a map can convey.  Identify some major types of map projections and discuss the advantages and disadvantages of each.

Advantages of a Globe  Earth is a sphere  Sizes and shapes of features are not distorted and distances are true to scale.  Most accurate way to show Earths surface curves.  Globes usually have a geographic coordinate system and a scale. The shortest distance between two points is the length of the arc (portion of a circle) that connects them.

How to measure distance on a Globe.  Globes usually have a geographic coordinate system and a scale. The shortest distance between two points is the length of the arc (portion of a circle) that connects them.  A location on a globe must be determined using polar coordinates because a globe is curved  Polar coordinate is useful on curved surfaces.

Disadvantage of using a Globe  Globes are difficult to make and carry around, and they cannot be enlarged to show the details of any particular area. As a result, people need maps.  So what is a map, a generalized view of an area, usually some portion of Earth’s surface, as seen from above at a greatly reduced size

Maps, visual representation of a surface with symbols indicating important features. Different types of maps contain different information. Examples of some maps that are important in Earth science are: Relief Map Radar Map (weather) Geological Map (rocks) Topography Map (Landscape/Elevation)

So why use maps? Maps are selective views of reality  Represent a larger area  Show what we can’t see  Present info concisely  Show spatial relationships  Size of the map relative to reality (scale)

Scale is a fraction on the area Larger area covered means larger denominator 1 inch equals 10 miles

Map Projections  are 2-dimensional (2D) representations of a 3-dimensional (3D) Earth. In a small area, Earth is essentially flat, so a flat map is accurate.  But to represent a larger portion of Earth, map makers must use some type of projection to collapse the third dimension onto a flat surface. A projection is a way to represent the Earth’s curved surface on flat paper.  A map projection translates Earth's curved surface onto two dimensions.

There are two basic methods for making projections:  The map maker “slices” the sphere in some way and unfolds it to make a flat map, like flattening out an orange peel.  The map maker looks at the sphere from a certain point and then translates this view onto a flat paper.

Mercator Projection  n 1569, Gerardus Mercator ( ) developed the Mercator projection  a flat piece of paper curves around the spherical Earth to make a cylinder. The paper touches the sphere at the equator, but the distance between the sphere and the paper increases toward the poles. The features of Earth’s surface are projected out onto the cylinder and then unrolled, creating a Mercator projection map. 

Conic Projection  A conic map projection uses a cone shape to better represent regions and best depicts the area where the cone touches the globe  A conic map projection wraps the Earth with a cone shape rather than a cylinder.

Gnomonic Projection  With a gnomonic map projection, paper is placed on the area that you want to map. The projection is good for features near that point. The poles are often mapped this way.  A gnomonic projection places a flat piece of paper on a point somewhere on Earth and projects an image from that point.

Robinson Projection  A Robinson projection more accurately reflects the size and shape of features near 45 degrees.  This projection has less distortion near the poles, and features within 45 degrees of the equator are closer to their true dimensions. The distances along latitude lines are true, but the scales along each line of latitude are different. Robinson projections are still commonly used.  A Robinson projection more accurately reflects the size and shape of features near 45 degrees

Winkel Tripel Projection  The National Geographic Society uses the Winkel Tripel Projection, which uses mathematical formulas to create a map projection that is also distorted at the edges

Rectangular Coordinates  Locations on a map are determined using rectangular coordinates  are useful for flat surfaces.

Lesson Summary  Maps and globes are models of the Earth’s surface.  Globes are the most accurate representations because they are spherical like the Earth is, but using a globe as a map has practical disadvantages.  There are many ways to project the three-dimensional surface of the Earth on to a flat map. Each type of map has some advantages as well as disadvantages.  Most maps use latitude and longitude to indicate locations.