map projections - usfwstraining.fws.gov/.../resources/map_projections_2013.pdf• understand the...
TRANSCRIPT
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MAP PROJECT IONS
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Map Projections
Session Objectives: At the conclusion of this session, you will be able to:
• Develop a rudimental knowledge of map projections and datums.
• Minimize distortion in map projections.
• Understand the difference between map projections and coordinate systems.
• Choose the appropriate projection and datum for your map.
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• “be afraid, be very afraid”Datums, Projections, and Coordinate Systems
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A spherical surface cannot be flattened without distorting it in several ways, so all maps must select and arrange distortions by means of a systematic transformation called a …
map projection
Map Projections
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Map ProjectionsProjection Surfaces
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Projecting data from a 3-dimensional surface to a 2-dimensional surface introduces …
distortion
Map ProjectionsDistortion
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• Shape• Area• Distance• Direction
Map ProjectionsKinds of Distortion
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• Shape : conformal projection • Area : equal‐area projection• Distance : equidistant projection• Direction : azimuthal projection
Map ProjectionsCorrecting Distortion
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Map ProjectionsDistortion Example
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Map Projections
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LAMBERT
Map Projections
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Map Projections
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Europe : 4 million square miles
South America : 7 million square miles
M E R C AT O R P R O J E C T I O NM E R C AT O R P R O J E C T I O N
AFRICA VS GREENLAND
Map ProjectionsArea Distortion
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Map ProjectionsCorrecting Distortion
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UTM – Universal Transverse Mercator
Map Projections
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UTM – Universal Transverse Mercator
Map Projections
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State Plane Coordinate System
Map Projections
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Projected Coordinate System:NAD_1983_StatePlane_Tennessee_FIPS_4100_Feet
Projection: Lambert_Conformal_ConicFalse_Easting: 1968500.00000000False_Northing: 0.00000000Central_Meridian:-86.00000000Standard_Parallel_1: 35.25000000Standard_Parallel_2: 36.41666667Latitude_Of_Origin: 34.33333333Linear Unit: Foot_US
Map Projections
State Plane Coordinate System
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Map Projections
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• You should choose a map projection that relegates distortion to places on your map that are not important to your message.
• At small scale, your projection choice will determine the overall “look” of your map.
Map ProjectionsHow this fits into Map Design
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Map ProjectionsHow this fits into Map Design
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• Wikapedia: A datum is a reference point on the earth's surface against which position measurements are made, and an associated model of the shape of the earth for computing positions.
• National Geospatial Intelligence Agency: A datum is a point, a line, or surface used as a reference in surveying and mapping. A geodetic datum is a mathematical model of the earth used to calculate the coordinates on any map.
Datums
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• NAD-27 : Clarke’s 1866 ellipsoid (best-fitted for the United States)
• NAD-83 : 1980 Geodetic Reference System GRS 80 (best fitted for the entire Earth)
Datums
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Datums
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Some final advice...
• Making a small scale map to display geographic features? Use a conformal projection such as Lambert Conformal Conic
• Making a map to perform area calculations? Use an equal area projection like Albers Equal Area.