Geography 417
California for Educators

Using the Geographic Grid

Objectives

• Students will identify and explain the geographic grid system.

• Students will use coordinates to locate positions on the earth’s surface.

• Students will find the coordinates of identified locations.

• Students will recall the basic components of the geographic grid.

The Geographic Grid

• The geographic grid is a coordinate system that is used to locate or identify place on the earth.

• Generally coordinate system employs latitude and longitude degrees as identifiers, although there are dozens of systems.

• Basis for system goes back to Eratosthenes in 247 B.C. who calculated the polar circumference.

• Formalized by Ptolemy.

• Based on the simple geometry of a the earth as a sphere.

Figure: The Geometry of the Grid System

Parallels of Latitude Meridians of Longitude

Latitude

• The angle measured in degrees, minutes and seconds created between any location on earth and the equator

360 ° = Circle

60' = 1 degree

60" = 1 minute

• Maximum value is 90° north and south of the equator

• Distance between 1 ° of latitude is 111 km (69 miles)

• Reference circle is the equator (0 °)

• Newer system is based on fractions of 10, not 60.

• Places frequently referenced as ‘high’ or “low” latitudes. We live in the ‘mid-latitudes’

Figure: Parallels of Latitude

Figure: Geometry of Latitude

Parallels of Latitude Meridians of Longitude

Longitude

• The angle measured in degrees, minutes and seconds created between any location on earth and the Prime Meridian

• Maximum value is 180 ° (International Date Line)

• Distance between lines of longitude varies

– 111 km (69 miles) at the equator and decreases towards the poles

• Reference meridian is the Prime Meridian (0 °) which runs through Greenwich, England

• Reflects the political power and England’s navigational needs.

Figure: Geometry of Longitude

Figure: Meridians of Longitude

International Date Line

Figure: Locate any point with Lat/Long

Figure 2: Earth with Graticule

Hemispheres

• Hemispheres are the “halves” of the earth.

• Northern hemisphere is that above the equator.

• Western hemisphere is that half which is west of the Prime Meridian and east of the International date line.

• Not to be confused with “The East” or “The North” or “The West”, which are perceptual regions.

Can you identify these?

Figure: Small Circle

Figure: Great Circle

Figure: Navigation with Great Circle

Projections

• Since the earth is spherical and maps are flat, it is impossible to map the 3D earth without creating distortions on a 2D map.

• All maps are distorted in at least 1 of 3 ways: Shape, Size or Direction.

• Can you identify the problems with each of the following projections?

Mercator Projection

Peter’s Projection

Goode Projection

Robinson Projection

Perspective is Important