Transcript Map projection

By Mrs. Page
(with a LOT of help from the Internet!)
Map Projections
• Map projections are attempts to portray the
surface of the earth or a portion of the earth
on a flat surface. Some distortions of shape,
distance, direction, scale, and area always
result from this process.
• The purpose, or function of the map,
determines what projection should be used
• The geographic location determines what
projection should be used
Centered at Lawrence, Kansas, the geographic
center of the “Lower 48” States
Centered at Ada, OK
The Geographic Grid
Latitude and Longitude
Latitude is measured north and
south of the equator, up to 90º
Longitude is measured east and west
of the Prime Meridian—meridian
that passes through Greenwich,
England—up to 180º
Visualizing Physical Geography
Copyright © 2008 John Wiley
and Sons Publishers Inc.
Map Projections
Many types of maps, for many different purposes
Visualizing Physical Geography
Copyright © 2008 John Wiley
and Sons Publishers Inc.
Map Projections
1:50,000
Map Scale
Scale fraction: a ratio that tells how
to convert distance on the map to
true distance on the Earth
Visualizing Physical Geography
Copyright © 2008 John Wiley
and Sons Publishers Inc.
1 unit of map
distance=50,000 units
of distance on the Earth
Map Projections
Map projection: a system of parallels and meridians representing the Earth’s curved surface
drawn on a flat surface
• Curved surface cannot be projected onto a flat sheet without distortion
• Each map projection has a specific purpose
• Each projection has advantages and drawbacks
Visualizing Physical Geography
Copyright © 2008 John Wiley
and Sons Publishers Inc.
Mercator Projection
•The Mercator projection has
straight meridians and
parallels that intersect at right
angles.
•Scale is true at the equator
or at two standard parallels
equidistant from the equator.
•The projection is often used
for marine navigation
because all straight lines on
the map are lines of constant
compass bearing.
Mercator is a
cylindrical projection.
Cartographers start by
wrapping a cylinder
around the globe along
the equator.
Original Mercator Projection Map, 1569
Map Projections
Mercator projection: map projection with horizontal parallels and vertical meridians
• Invented 1569 by Gerardus Mercator
• Used for navigation
• Scale increases from equator to poles
• Straight line on the map is a line of constant compass bearing
• Straight line on a Mercator projection not the shortest distance between two points
Visualizing Physical Geography
Copyright © 2008 John Wiley
and Sons Publishers Inc.
Robinson Projection (1961)
•Neither conformal nor equidistant
•Compromises shape and size
•Longitude lines are curved
Robinson Projection
This grid plot shows the distortion factor of the Robinson projection.
The Robinson projection with Tissot's Indicatrix of deformation
Mercator
Projection
Notice shapes and sizes!
Robinson
Projection
Map Projections
Goode Projection: Equal-area map projection often used to display
information such as climate or soil type
• Shows true sizes of regions on Earth’s surface
• Distorts shapes of places, especially high latitudes and at edges of map
•Called an “interrupted projection”
Visualizing Physical Geography
Copyright © 2008 John Wiley
and Sons Publishers Inc.
This is sometimes called an “orange
peel” projection. Can you guess why?
Map Projections
Azimuthal (polar) projection: map projection centered on Earth’s North or South Pole
• Used for maps of polar regions
• Scale increases outward
• Shows only one hemisphere
Visualizing Physical Geography
Copyright © 2008 John Wiley
and Sons Publishers Inc.
Lambert Azimuthal Equal-Area Projection
•Maps from a sphere to a disk.
•It accurately represents area in all regions of the
sphere, but it does not accurately represent angles.
•It gives a planar picture of the sphere in which every
region appears with the correct area but perhaps a
greatly distorted shape.
Here’s an azimuthal projection from the
South Pole. What continents do you see?
Unusual Map Projections
Works Cited
•Morehead State University
http://people.moreheadstate.edu/fs/j.holcomb/praxis.pdf
•Progonos Project
http://www.progonos.com/furuti/MapProj/Dither/ProjAz/
projAz.html
•University of California at Santa Barbara
http://www.ncgia.ucsb.edu/projects/tobler/Projections/sl
d012.htm
•Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.