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Maps. What is a map?. A Map is a two or three-dimensional model or representation of the Earth’s surface. 2-Dimensional map. What is a “Map Projection”?. Planar Projection. Projection.
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What is a map? A Map is a two or three-dimensional model or representation of the Earth’s surface. 2-Dimensional map
What is a “Map Projection”? Planar Projection
Projection A Projection is a mathematical means of transferring information from the Earth’s three-dimensional curved surface to a two-dimensional map.
Types of Map Projections All map projections are “flawed” by distortions that are created during “projection”. Different map projections have been developed to reduce this distortion to different areas of the map for different purposes.
Map Distortions Greenland Mercator map size True size of Greenland
Latitude and Longitude Where am I? Early Greeks and Chinese attempted to create a grid system to help them answer this question. But it was not until the Middle Ages that the latitude/longitude system was developed.
Latitude and Longitude Cartographers (mapmakers) have established a set of vertical and horizontal grid lines that cover the globe called: Parallels- Lines of Latitude are horizontal lines on a map that show latitude, positions north and south of the equator. Meridians- Lines of Longitude are vertical lines on a map that show longitude, positions east and west of the prime meridian. Because the Earth is a sphere, each line represents a 1 degree slice of the 360 degrees in a the sphere.
The Earth can be divided into vertical and horizontal halves called Hemispheres.
The Equator-Divides Northern and Southern Hemisphere Equator
The Prime Meridian-Divides Eastern from Western Hemisphere. Prime Meridian
Latitude Line “Rules” • Run East to West • Measure distance in degrees from the Equator • Each line forms a circle around the Earth that is vertically equidistant from the equator. • Numbered from 0 to 90 Degrees • (0 being the equator, and 90 being the poles)
Lines of Longitude Prime Meridian
Longitude Line “Rules” • Run North to South • Measure distance in degrees from the Prime- Meridian • Form half-circles that are equidistant from each other at the Equator, but converge at the poles. • 0 Degrees Longitude is at Greenwich, England (established in 1883); 180 Degrees is in the Pacific, and is called the International Date Line • (divides the Globe between two days).
The Degree is the basic unit of Latitude and Longitude A general location on the globe would be shown as 45 N. A more precise location on the globe would be 45 15’ 35” N.
How “big” is a Degree? Each degree in Latitude and Longitude is approximately 69 miles “wide” at the equator. Each degree can be divided into 60 subdivisions called minutes(1.15 miles in “width”). 45’ Each minute can be divided into 60 subdivisions called seconds (.019 miles, or 100 feet!). 35” So, your location on the globe can be very precisely identified, and would look like this: 97 35’ 42” W.
Every spot on Earth has an address that is determined by referencing, in degrees, minutes and seconds, the latitude and longitude of that location.
Map Scale Map Scale expresses the relationship between the distance on a map and the true, corresponding distance of the same area of the Earth’s surface. Mapmakers can't draw maps the same size as the area they represent; the maps would be too big. So they draw features smaller than they actually are.
A map scale is usually given as a fraction (1/10000) or a ratio (1:10000) USGS maps contain scales that have the same units on both sides of the ratio. Fractional scale
The larger the number on the right, the greater the amount of land that the map represents.
Bar Scale A bar scale is just a line drawn on a map of known ground length. There are usually distances marks along the line. Bar scales allow for quick visual estimation of distance.
Pay attention to where the zero point on the bar actually is when you measure with a bar scale! Notice that 0 is here!
Map Orientation • Orientation is determined by Cardinal directions • of North, South, East and West. • A compass is usually to determine the cardinal • directions on the ground. • A compass does not normally point to true north. • Only in a few places does True North and Magnetic • North line up with each other. The direction in • which the compass needle points is referred to as • Magnetic North, and the angle between magnetic • north and true (geographical) north direction is called • Magnetic Declination.
Topographic Maps Topographic Maps
A Topographic Map is the representation, normally on a flat surface,of part of the Earth’s surface, drawn to scale.
Topographic maps show distance relationships and elevation. Topography actually means, “the shape, elevation and slope of the land”.
Topographic Maps Different symbols and colors are used to indicate various features on topographic maps, including bodies of water and human-made structures. A topographic map of Portland, Maine shows various physical features of the area.
Topographic maps also include symbols that represent such features as woods, houses and roads. House Woods Streams Roads
One of the main features of topographic maps are contour lines.
We could start with an island, and increase the level of the ocean the amount of our contour interval, an marking the shore line as we raise the water level.
10 feet above normal sea-level Notice that the shape of the island changes. Why?
Contour Lines are Imaginary lines that join points of equal elevation on the land above or below sea level. All points on this line have an elevation of 250 feet above sea level, for example.
There are several different kinds of contour lines. Index Contour (darker, has elevation) Intermediate Contour (lighter; does not have elevation identified)
Depression Contour Lines Perp. Lines point downhill, into the depression Lip of depression is highest point
280 260 **Edge of depression is between 240-260. 220 240
Contour Lines make it possible to determine the shape of the land without looking at the actual spot. Ridge Valley
