map projections used to transfer the image of the earth’s surface onto a flat surface no...
TRANSCRIPT
Map Projections
• used to transfer the image of the earth’s surface onto a flat surface
• no projection is an exact representation
• generally, the larger the area, the larger the distortion
• the 3 most common projections are cylinders, cones and planes
Cylindrical Projections
Mercator Projections • results when the contents of a globe are
transferred onto a cylinder of paper
Conic Projections• made by transferring the
contents of a globe onto a cone
• distortion increases north to south
• best used for land masses that have more area east to west (USA) than north to south (South America)
Planar Projections
Azimuthal Projections• made by transferring the
contents of a globe onto a plane
• the plane touches the globe at only 1 point, usually at the poles• very little distortion at that
point• distortion of direction,
distance and shape increase as the distance from the point of contact increases
West Wing Map Projection Clip
• http://www.youtube.com/watch?v=n8zBC2dvERM
Modern Map Making
Aerial Photographs
• taken from planes
• are very important to map makers in making accurate maps
• allow for a different perspective
Remote Sensing
• the gathering of information about a place without being there
• cameras in planes, satellites with sensors
• allow for very accurate maps
Information shown on maps
Title
• tells what area is being shown on the map or gives information about the map subject
– A Map of the Coast of East Florida from the River St. John Southward near to Cape Canaveral – 1791
– A Map of the New Governments of East and West FLORIDA. Inset of Pensacola – 1763
– A map of the peninsula of Florida showing the present field of surveying in the territory - 1846
– A Map of the Southern Indiana District of North America - - - Manuscript in Ayer Collection at the Newberry Library –1775
– A Map of the WEST INDIES... - 1715
Map’s scale
• shows the relationship between the distance on the earth’s surface and the distance on the map
Graphic scale “map’s ruler”
• the distance on the earth’s surface is represented by a bar graph that shows units of distance
Verbal scale
• is a phrase that describes a measure of distance on a map relative to the distance on the earth’s surface
UNITS VERBAL SCALE
inches 1 inch on the map = 62500 inches on the ground.
feet 1 foot on the map = 62500 feet on the ground
cm 1 cm on the map = 62500 cm on the ground
m 1 m on the map = 62500 m on the ground
Representative fraction • a fraction or ratio that shows the
relationship between the distance on the map and the distance on the earth’s surface
• it is unitless• it remains
constant no matter the measurement used
Compass rose
• shows how the map is positioned in relation to true north
Legend
• is a list of symbols used on the map and their explanations
Date
• gives the time at which the information on the map was accurate – County Map of Florida - 1872 – County Map of Florida - 1882
Topographic map • a map that shows surface features
(topography) of the Earth• natural features like rivers, lakes,
mountains• man made features
like cities, roads, bridges
• also show elevation
Elevation
• the height of an object above sea level
• sea level is 0
Topographic maps of the entire US were prepared by the Unites States
Geological Survey (USGS)
Contour lines • are lines that connect points of equal elevation
• are used to show elevation• the closer the contour
lines, the steeper the slope
• the more spread out the contour lines, the flatter the slope
• contour lines never intersect
contour interval • the difference in elevation between contour
lines• contour interval is chosen according to the
area’s relief
relief
• the difference in elevation between the highest point and the lowest point being mapped
index contour
• a darker, heavier contour line (usually every 5th line) that is labeled by elevation
• makes reading the map easier
hachures
• short, straight lines within a contour line
• indicate a depression
Reading a Topographic Map
Step 1 Contour lines never cross; all points along a
contour line are of the same elevation
Step 2 Closely spaced contour lines indicate a very
steep slope; widely spaced contour lines indicate a subtle slope
Step 3 Contour lines crossing valleys or streams
are “V” shaped. The “V” points to the higher elevation. If there is a river or stream in the valley, the “V” indicates the upstream direction.
Step 4Contour lines formed closed loops around hills,
mountains and depressions. Check for hachures.