Models of the Earth

Chapter 3, Section 1 - Finding Locations on Earth                                                                                                                                   

Axis - The imaginary line around which the Earth rotates.
    [ globe showing parallels ]
  • The places where the axis meets the surface of the Earth are the geographic North and South Poles.
  • Halfway between the poles is the equator, which divides the Earth into Northern and Southern Hemispheres.
Parallel - Any circle that runs east-west around the Earth and is parallel to the equator.  (A line of latitude.)
Latitude - The angular distance north or south of the equator, expressed in degrees.
  • 0o Latitude = Equator
  • 90o North Latitude = North Pole
  • 90o South Latitude = South Pole
Each degree of latitude...
  • equals about 111km.
  • can be divided into 60 minutes (60').
    • each minute can be divided into 60 seconds (60").
Meridian - Any semicircle that runs north-south around the Earth from pole to pole.  (A line of longitude.)
Longitude - The angular distance east or west of the prime meridian, expressed in degrees.
[ globe showing meridians ]
  • 0o Longitude = Prime Meridian (runs through Greenwich, England).
  • 180o Longitude is opposite the Prime Meridian.  Others are labelled as E or W of the Prime Meridian.
Each degree of longitude...
  • can be divided into minutes and seconds.
  • is about 111km at the equator, but gets smaller as you approach the poles.
Great Circle - Any circle that divides the globe into two equal halves.
  • Can occur in any direction.  (Planes tend to fly along them.)
  • Any two lines of longitude that are directly across from each other.
  • The equator is the only latitude line that is a great circle.
[ exploded globes showing great circles ]
Finding Direction
  • Magnetic compass - points towards the magnetic poles, which are slightly different than the geographic poles.
  • Magnetic Declination - The angle between the direction to the geographic North Pole and the magnetic North Pole.  This changes constantly.
  • Global Positioning System (GPS) - A satellite navigation system that uses signals from three satellites to pinpoint a person's location.

Chapter 3, Section 2 - Mapping Earth's Surface                                                                                                                                       

Cartography - The science of making maps.
  • Data for making maps is gathered through...
    • Field Surveys - Cartographers walk/drive through an area, taking measurements.  Data is then plotted on a map.
      • Measurements are estimated for sites between survey points.
    • Remote Sensing - The process of gathering and analyzing information about an object without being in physical contact with it.
      • Uses images from satellites and airplanes.
Map Projection - A flat map that represents the curved surface of the globe.
- No projection is completely accurate.  The larger the area covered, the greater the distortion.

Types of Map Projections
For each of the following, imagine a globe of the Earth with a light bulb inside.  Surface features and lines of latitude and longitude are projected onto a piece of paper.  How the paper is held up to the globe determines the type of map projection.
  • Cylindrical Projections
    • The paper is wrapped into a cylinder around the Earth.  (Touches at equator.)
    • Lines of Latitude/Longitude form a grid, making them easier to use.
    • Areas near the equator are accurate; distortion increases as you near the poles.
    • Distortion is minimal for small areas.
  • Azimuthal Projections
    • The paper is held flat, touching only one place on the globe.  (Usually at a pole.)
    • Little distortion at point of contact; increases as you move away.
    • On this projection, Great Circles appear as straight lines.
      • Useful for plotting airplane routes.
  • Conic Projections
    • The paper forms a cone and is placed over the globe so that cone's axis lines up with Earth's axis.  (Touches at one parallel.)
    • Most accurate where the cone touches the globe.
    • Polyconic Projection - Using a series of overlapping Conic Projections to increase accuracy.

Reading Maps
  • Directions
    • Compass Rose - A symbol showing North, South, East and West (the cardinal directions).
      • Sometimes only an arrow indicating North is shown.
    • Parallels and Meridians - Lines of Latitude and Longitude, which are used to show directions.
  • Symbols
    • Legend - A list of map symbols and their meanings.
  • Scale
    • The relationship between the distance shown on a map and the actual distance.
      • Graphic Scale - A printed line with markings that represent units of measure (mile, kilometer, etc.)
      • Fractional Scale - A ratio of map units to actual units.  1:25,000  (1 cm on the map = 25,000 cm on Earth)
      • Verbal Scale - Expresses scale in a sentence.  "One centimeter is equal to one kilometer."
  • Isograms
    • A line on a map that indicates constant/equal value.
      • Isotherm - Line that runs through areas with the same temperature.  (Used for locating air masses.)
      • Isobar - Shows areas with equal air pressure.
      • Contour lines - Show areas with the same elevation.

Chapter 3, Section 3 - Types of Maps                                                                                                                                                     

Topographic Maps
Topography - The size and shape of land surface features (including its relief).
Elevation - The height of an object above sea level.
Mean Sea Level - Halfway between the highest and lowest tide levels.  
   Elevation is based on this.

Contour Lines - Isograms that connect areas of the same elevation on a map.
Contour Interval - The difference in elevation between one contour line and the next.
Relief - The difference between the highest and lowest elevations in the area being mapped.
Index Contours - Every fifth contour line on a map, which is bolder and labelled with the elevation.
Elevations of specific points on a map are labelled with an x.

Reading Contour Lines
  • If the contour lines are spread out, this indicates gentle slopes.
  • If the contour lines are close together, this indicates steep slopes.
  • Contour lines that form a V indicate a valley.
    • The point of the V is at the high end of the valley.  (The V points upstream, if there is water flowing through it.)
  • Contour lines that form closed loops indicate a hill or depression.
    • A depression is shown with depression contour lines, which have perpendicular lines on them that point towards the center of the depression.
Topographic Map Symbols
  • Contour lines are black or brown.
  • Constructed objects (buildings, roads, boundaries, railroads) are black.
  • Bodies of water are blue.
  • Forested areas are green.
  • Areas updates by aerial photographs, but not verified by field exploration are purple.

Geologic Maps
  • Show the distribution of geologic features, such as rock types, faults, folds, etc.
  • Printed over a base map, which shows topography, roads, etc. to help identify the location of the geologic structures.
Geologic Unit - A volume of rock of a certain age and type.  On a geologic map, these are shown with...
  • Color - similar ages may have different shades of the same color.
  • Letters - one capital letter (symbolizing the rock age) followed by two or three lower-case letters (symbolizing the name of the unit OR type of rock).
Contacts - Places where two geologic units meet.  These are shown with contact lines.  
Two main types of contacts are...
  • Depositional Contacts - Places where one rock layer formed over another.
  • Faults - Cracks where the rock has moved past each other.
Strike - Indicates the direction that a rock bed runs.
Dip - Indicates the angle at which the rock bed tilts.

Soil Maps
  • Used to classify, map and describe soils.
  • Based on soil surveys - generally at the county level.
  • Natural Resources Conservation Service (NRCS), part of the US Dept of Agriculture (USDA), is responsible for compiling and and mapping soil data.
Soil Surveys contain text, maps and tables...
  • The text contains general information on the geology, topography and climate of the area.
  • The tables describe the types and volumes of soils in the area.
  • Two types of maps...
    • A very general one that shows approximate areas of different types of soils in the area.
    • One with more detailed information.
Soil maps are used in agriculture and land management, to plan land usage and soil conservation.

Other Types of Maps
Earth scientists use also use maps which show...
  • Location and movement of air and water.
  • Air pressure and weather systems.
  • Amount of rainfall in an area.
  • Flow of groundwater.
  • Changes in topography over time.
  • Changes in available resources.
  • Changes in climate.


Chapter Assignment
  Pg. 78-79 #5-17, 19-23, 35-37.