Chapter 3. Models of the Earth In order to locate points on Earth, we use models. Two general types of models: Maps Globes 2-Dimensional3-Dimensional More portableLess portable Less accurateMore accurate To find points on a map/globe, we use coordinates.

Latitude lines

Lines of Latitude or Parallels A set of circles that run parallel And describe positions North or South of the equator. Equator = 0 o latitude North and South poles are each 90 o N or 90 o S Washington, D.C. Is 38 o 53’ 40” N. Read as 38 degrees, 53 minutes, and 40 seconds North Latitude is always written first when recording coordinates and is always North or South.

Longitude lines

Lines of Longitude or Meridians A set of ½ circles that run vertically (up and down) Lines of longitude meet at the poles. And describe positions East or West of the Prime Meridian Prime meridian = 0 o (runs through Greenwich, England) West of the Prime meridian  0 to 180 o W East of the Prime meridian  0 to 180 o E International Date Line = 180 o, exactly ½ around the globe from the Prime Meridian – it marks the place where each new day officially begins at midnight. (It would be noon on the previous day at the Prime Meridian) Washington, D.C. 77 o 02’ 12” W – Read as 77 degrees, 02 minutes, and 12 seconds West Longitudes are always written second and have East or West coordinates.

Map Projections A map is a flat representation of Earth’s curved surface. A map projection is a method used to transfer features on a 3D globe onto the flat surface of a 2D map. Results in a distorted image of the curved surface. Distortions may occur in size, shape, direction, and distance. The larger the area being shown, the greater the distortion.

Cylindrical map projection Mercator projection

Cylindrical or Mercator Projections Created by forming a cylinder around the earth. Most common type; used for making world maps Advantage: Accurate at the equator Advantage: parallels and meridians form a grid which makes locating positions easier. Advantage: The shapes of small areas are well preserved. Good for making maps of small areas. Disadvantage: distorts distances near the poles Disadvantage: distorts sizes near the poles Greenland appears larger than South America.

Conic map projection

Conic Projections Created by forming a cone at any location on a globe. Advantage: Can make a map of anywhere on the globe. Advantage: Areas near the points of contact (parallels) are least distorted. Advantage: The relative size and shape of small areas on the map are nearly the same as those on a globe. Disadvantage: areas farthest from the points of contact show the most distortion.

Azimuthal (or Polar) map projection

Azimuthal (or Polar) Projections Created with only one point of contact. Commonly the one point of contact is the north or south pole; this is known as a POLAR projection. Advantage: Good to use for polar views. – Important in air travel in these areas. Advantage: Little distortion at the point of contact Disadvantage: unequal spacing between parallels that causes a distortion in both direction and distance. Disadvantage: distortion increases as distance from the point of contact increases.

The Global Positioning System “GPS” A satellite navigation system that is based on a global network of 24 satellites that transmit radio signals to Earth’s surface. NAVSTAR (1978) first GPS satellite launched. A personal receiver (like your phone) on the earth receives data from three satellites to calculate latitude, longitude, and altitude. Accurate to m of actual position. High tech receivers can be accurate to cm.

Reading a Map Direction on a map: – look for compass directions (N is at the top, east is right, west is left, and south at bottom) – Designated by arrows or compass rose. – Show cardinal directions – N, S, E, W. – Compass rose:

Reading a map: Map symbols find the legend which shows a list of the symbols and their meanings.

Map scales Shows the relationship between distance shown on the map and actual distance. Graphic scale – much like a ruler. Fractional scale – shows distance as a ratio. Verbal scale – expresses scale in a sentence. Graphical Scale Verbal Scale Fractional Scale