Maps and Map Projections
How Maps Can Mislead Us
A Globe
• Is the only truly accurate
representation of the earth
A flat surface
• It is easy to portray a
flat surface on a flat
piece of paper
But there is no way to
accurately portray a
3-dimensional round surface
on a flat piece of paper
• Therefore all maps are distorted
Distortion will occur in at least one
of these map components:
•
•
•
•
Size (area)
Shape
Distance
Direction
Making Maps
• Mapmakers have devised many different
methods for making maps of the world
Projections
• The different methods
are called
“projections”
• The term projection
refers to projecting
the 3-dimensional
globe onto a flat
surface
Equivalent
• A map that is equivalent is accurate in
size or area
• It is NOT going to be accurate in shape
Peter’s map is equivalent
Conformal
• A map that is conformal is accurate in
shape
• It will NOT be accurate in size (area)
Mercator map is conformal
A world map cannot be both
equivalent and conformal
• Equivalence and conformality are mutually
exclusive properties
Common Map Projections
•
•
•
•
Cylindrical
Conical
Planar or polar
Compromise
Tangency
• Each projection is accurate at
the point(s) of tangency only
– Cylindrical: equator (line)
– Conic: mid latitude (line)
– Planar: one pole only (point)
• Further away from point(s) of
tangency = more distortion
Cylindrical
Cylindrical Projections
• Common for world maps
• Distorts size (area) more in areas farthest
away from the equator
• Distortion greatest in northern latitudes
– most of the northern hemisphere’s land mass
is far from the equator
• Mercator is the most common cylindrical
projection
Conical
Conical Projections
• Best for continents in mid latitudes
– North America
– Europe
– Russia
• Not useful for a world map
– Unless several are put together
Planar or Polar (Azimuth)
Polar Projections
• Only one hemisphere
• Arctic Ocean in the northern hemisphere
• Antarctica in the southern hemisphere
• Not good for mid latitudes, low latitudes
don’t show at all
Compromise Projections
• Minimize distortion in one aspect AND
• Keep the most accuracy in other aspects
– Mollewide
– Robinson
– Goode’s Homolosine (interrupted)
Robinson
Mercator
Mollewide
Distortion
Compared
Scale
• All maps have a scale
• Scale relates map size to actual earth
size
• A scale of 1:10,000 means that one unit of
measurement on the map will equal tenthousand of the same units on the surface
of the earth
Legend
• The legend is the key to reading the map
– Defines the colors and symbols
• Map scale will be in the legend or at the
bottom of the map
– Ratio
• 1:10,000
– Fractional
• 1/10,000
– Words
• “One inch equals ten-thousand inches”
– Graphic – looks like a ruler
Large Scale vs. Small Scale
• A large scale map portrays a small part of
earth’s surface
– City
– Campus
– Classroom
Cholera Map of London
City Map of Denver
• A small scale map portrays a large portion
of earth’s surface
– World map – the smallest scale of all
– 1:13,000,000 is the scale of our wall map
Scale and Distortion
• The smaller the scale of the map, the
larger the portion of earth’s surface is
being shown
• The larger the portion of earth’s surface,
the more curvature
• The more curvature, the more distortion
will occur in transposing it to a flat map
Extremely small scale maps,
like world maps, have the
most distortion
• Large scale maps, like a map of the college
campus, have little or no distortion
Types of Maps
• Maps are generally made for a
specific purpose
Road Map
• Roads, towns, cities,
and other data useful
for transportation
• Most familiar type of
map to the average
person
• But there are many
other types of maps!
Political
• Show man-made divisions, such as the borders
of states or countries
Political vs. Physical
Physical
• Show physical characteristics, like mountains,
lakes, and rivers
• Often show elevation by color coding
Topographic
• Shows landforms and elevations in detail
Contour lines - lines that connect places with
equal value, in this case “feet above sea level”
Thematic
These maps each have a special theme
• Physical
– Climate
– Ocean Currents
– Biomes
• Cultural
– Population
– Ethnicity
– Income
Map of World Population