Chapter 3 Models of the Earth

Finding locations on Earth Since Earth almost perfect sphere, no reference points to specify locations. SO…….. We use Earth’s axis of rotation to set up a grid to designate locations.

Setting up the grid Equator: Halfway between the poles; dives the globe into north and south Parallels: Set of circles that describe positions north and south of the equator. Latitude: The angular distance worth or south of the equator. Because from the equator to the pole is ¼ of the total globe and a globe is 360 degrees around, equator to the pole is 90 degrees, north or south. Degrees of latitude further broken down into minutes and seconds in order to allow for precise locations.

Setting up the grid (cont…) Meridians: The half circles/vertical lines running pole to pole that the tell us how far east and west a location is. Prime Meridian: Runs through Greenwich, England and is the designated 0 degrees. Longitude: Angular distance in degrees, east or west from the prime meridian. Because Earth is 360 degrees, the point on Earth opposite the prime meridian is 180 degrees. All longitudes are between 0 and 180 degrees either east or west of the prime meridian. Great Circles: any circle that divides the globe into halves.

Finding direction Magnetic compasses: Point to magnetic poles. Magnetic poles and geographical poles are located in different places. Magnetic Declination: The angle between the direction of the geographic pole and the direction in which the compass needle points. (Approx. 10 degrees) Because magnetic north changes over time, declination also changes over time. This is why we use geographic north for mapping. Global Positioning System (GPS): Satellite navigation system based on global network of 24 satellites. Military GPS accurate to within centimeters.

Mapping earth’s surface Cartography: The science of making maps. Cartographers: Scientist who make maps. Methods used by cartographers: 1. Field surveys in which information is collected and information is plotted on map. 2. Remote sensing: Equipment on satellites or airplanes obtain images. 3. Both are combined to create maps.

Map projections: A flat map that represents the 3-D curved surface of earth. All maps have distortions. Cylindrical: As if you placed piece of paper around the globe and traced. (touches at Equator) Accurate near equator and more distorted toward poles. Conical: As if cone places over globe. (touches at one latitude). Most accurate Near latitude it touches. Azimuthal (Plane): As if paper touches at only one point. Further away from this point, the more distortion.

Reading a map Typically: Maps are drawn with north to the top, west at the left, east to the right, and south at the bottom. USGS (United States Geological Survey), maps drawn with parallels and meridians. Compass rose labels the cardinal directions (N,S,W,E) Symbols: Will be explained in the map legend. Map Scale: Shows distance. Graphical scale shows a “ruler” with markings. Fractional scale shows proportions, such as 1:100 where 1 unit on map represents 100 units on Earth. Fractional scales work with any measurement unit. Verbal scale expresses scale in sentence form (i.e. One centimeter is equal to one kilometer.)

Isograms Isogram: A line on a map that represents a constant or equal value iso- means “same” or “equal” -gram means “drawings” Examples: isotherm map: shows areas with same temperature Isobar map: shows areas of same pressures

Types of maps Topographic Maps: Show both natural features and constructed features. Made from using both aerial photographs and survey points collected in the field. Shows elevations. All elevation measured from sea level. Advantages: Shows a land areas size, shape and elevation.

Types of maps (topographic maps…. Cont…) Contour lines: Show points with equal elevation. Because points of equal elevation are connected, the shape of the contour lines show the shape of the land. Contour interval: The difference between one contour line and next. Relief: The difference in elevation between the highest and lowest areas. Index contours: Bold lines (every 5 lines) that make map easier to read.

Geologic maps Show the distribution of geologic features, such as types of rocks and locations of faults, folds and other geological structures. Usually drawn on top of a base map that shows surface features, roads, and other locations as reference.

Geologic maps… cont….. Rock Units: A volume of rock of a given age range and rock type is a geologic unit. On geologic maps, geologic units are shown in different colors based on ages. Other structures shown: Contact lines: Where two units meet. Faults: Cracks where rocks can move past one another. (Strike and dip may be labeled.)

Soil Maps Soil scientist construct soil maps to classify and describe soils. Based on surveys. Soil maps are valuable tools for agriculture and land management. Helps farmers, ag engineers, and governmental agencies identify ways to conserve and use soil and plan site for future development.

Other types of maps Meteorologist: Use to plot precipitation and air pressure. Satellite images used to locate and plot direction of water flow in order to determine future shortages. Used to track changes of Earth’s surface.