Transcript (Cartography)

CARTOGRAPHY
The Science and Art of Map Making
SOME
BASICS
A map is a two-dimensional or flat-scale model of the
earth’s surface.
Map Scale is the relationship between the size of a
feature on a map and the size of that same feature on
the earth
Cartography is the science AND ART of mapmaking
Scale is often represented in ratio/fraction, written or
graphic (bar graph) form
When comparing map scales, a small scale map means that
a very big section of the earth is shown (above, top) and a
large scale map means that a little area is show (above,
bottom)
EARLY
MAPMAKING
ARISTOTLE
ERATOSTHENES
Earth’s shadow is circular
First coined “geography”
Matter falls to center
Found earth’s circumference
Stars move with travel
Prepared earliest map of
world with five principle
climate regions
Earth is spherical
FEI XIU
Produced detailed map of
China in 267 BCE
AL-IDRISI
World map and geography
text in 1154 CE
Ibn-Battutah wrote a
travelogue spanning 75,000
miles and 30 year
AGE OF
EXPLORATION
Columbus
Magellan
De Gama
European geographic studies had died during the middle ages.
It began to revive again towards the Renaissance.
Europeans rediscovered Ptolemy’s maps and writings.
Cartographers took explorer’s information to make better maps.
17th Century maps displayed accurate outlines of most continents and oceans.
TYPES OF
MAPS
Maps display information
by location.
Cartographers choose
the type of information
they want to choose and
they way they want to
display it.
General maps (like road
maps) display a variety of
information.
THEMATIC MAPS are
designed to show a
particular theme (type of
information) that is
associated with certain
areas.
The above map displays shipping lanes in blue and the time it takes
to deliver packages to various regions in shades of brown to yellow.
Thematic maps can
display physical, social,
political, cultural,
sociological, economic,
agricultural, etc. aspects
of a region.
DOT
DISTRIBUTION
USES:
Shows exact location of the chosen theme
Shows distribution (concentration or dispersion) of the
theme
Shows patterns
Often used to show number by location (population of a
theme) at local scale
WEAKNESSES:
Poor differentiation in areas of high concentration
US Cell Phone Tower
Locations
CHOROPLETH
MAPS
USES
WEAKNESSES
Shows various classification levels of a chosen theme
Low number of classes causes distortion
Shows theme at regional (not local) level
High number of classes causes confusion
Compares regions in terms of chosen theme
Causes induction due to regional emphasis
ISOLINE
MAPS
ISOLINE
MAPS
Isoline maps attempt to show environmental factors that have height (ex: altitude) or that have increases and decreases in a measurable
value (ex: temperature, barometric pressure). Each line on the map represents the intersection of the maps surface with a horizontal plane
representing a thematic value (altitude, temperature, etc) at that point. The lines allow the reader to infer slope. ANY COLOR IS SIMPLY TO
PROVIDE CONTRAST FOR CLARITY.
USES
WEAKNESSES
Connects points of equality with a chosen theme
Difficult to differentiate in areas of high concentration
Good for displaying measured values (usually
environmental factors)
Low number of classes causes induction
High number of classes causes confusion
Temperature, elevation (relief), rain totals, weather
patterns, etc.
ISOLINE
MAPS
Topographic
Map
HISTORY
A topographic map (Topo) is a cross between a general map
and an isoline map.
They’ve been in existence since the 1600’s.
THE United States Geological Survey (USGS) is responsible
for making topos in the US.
There are over 54,000 topo maps covering the entire US.
USES
Used to show both the human and the physical landscape.
Typical scale is 1:24,000 inches.
Various symbols denote the human landscape.
Various colors, symbols and lines represent the physical landcape.
Isolines are used to show elevation (relief) of the land.
GRADUATED
SYMBOL
MAP
USES
WEAKNESSES
Shows amount (volume, size, number, etc. by class)
Overlapping symbols cause confusion
Shows location (local, regional, etc.)
Symbolization can trigger bias
Allows for comparison
MODERN
CARTOGRAPHY
Once a cartographer decides on the scale of his map (large scale or small scale) , he has to make some hard choices: what to leave
out, how represent thematic data, and how many classes of data to represent.
These decisions will make maps inherently inaccurate since they will not show the world as it really is.
Maps can be inaccurate in four ways:
SIMPLIFICATION
INDUCTION
CATEGORIZATION
SYMBOLIZATION
SIMPLIFICATION
Simplification occurs when a map omits
details that aren’t relevant to the purpose of
the map… roads, terrain features, etc.
Simplification can also mean that curved
roads get straightened and two points that
are far apart get closer together.
Check out the
simplification in
this map from the
Dallas Airport to
then site of a
wedding.
INDUCTION
Induction is a phenomenon associated ONLY with choropleth map.
A choropleth map shades a region a certain color that corresponds to the dominant trait
in that region. Even though not all of the people in the region display that trait, the map
makes it appear as if everyone does.
On choropleth maps, the minority is inducted into the majority trait.
Consider the below maps of the 2004 presidential election.
The first awards counties to the majority vote-getter.
The second awards states to the majority of counties.
The third awards the country to the majority electorate.
Consider how induction works at each level.
CATEGORIZATION
Categorization also occurs only with chorolpleth maps.
When a cartographer chooses the maps theme (population density by state on the maps below) he chooses not only the number
of classes to display, but also the dividing lines of the classes. The choice can radically alter the viewers perception and opinion.
According to each map, where do people live?
Map 1?
Map 2?
Map 3?
SYMBOLIZATION
Symbolization occurs with basic and
graduated symbol maps.
The cartographer chooses the symbols
that will represent various map features,
and those symbols can distort the
viewer’s opinions and perceptions.
The map at left uses red
dots to symbolize
cholera victims. How
would your perceptions
change if he had chosen
a skull and crossbones?
A daisy?
PROJECTIONS
Reality:
Earth is a sphere
Earth is a nearly perfect sphere, and a globe is an accurate, scale model of it.
THE PROBLEMS
A useful globe would be too large to manage
A globe can’t fold for easy transportation
A globe is too large to fit you your pocket,
glovebox, etc.
PROJECTIONS
The Solution:
Make the
world flat
A projection is a method for taking the 3D earth
and transferring its image onto a 2D (flat) surface.
THE PROBLEMS
A sphere is hard to flatten.
The process of making the flat surface DISTORTS
size, distance and direction on the flat map.
PROJECTIONS
All projections cause distortion:
SHAPE (more elongated or squat)
DISTANCE (between two objects increases or
decreases)
RELATIVE SIZE (looks larger or smaller than it is)
DIRECTION (not accurate between two places)
PROJECTIONS
DISTORTION
SHAPE
PROJECTIONS
DISTORTION
Which is bigger, the US or Greenland?
TOTAL LAND AREA (ACTUAL)
SIZE
GREENLAND
US
2,166,086
#12 in the world
9,826,675 sq km
#3 in the world
PROJECTIONS
DISTORTION
DISTANCE
HOW FAR IS IT
FROM SOUTH
AMERICA TO
AFRICA?
PROJECTION
TYPES
Equal Area Projections
PROS
CONS
Relative size of landmasses is the same as in
reality
To preserve size and shape, map must interrupt
eastern and western hemispheres
Most shapes are not distorted, but areas
towards the north and south poles become
distorted
Meridians do not converge on the map and do
not form right angles with the parallels
PROJECTION
TYPES
Mercator Projections
PROS
Very little shape distortion
Direction is consistent
Map is a nice, neat rectangle
CONS
Area towards poles is grossly distorted (larger)
PROJECTION
TYPES
Robinson Projections
PROS
CONS
Visually pleasing
Does not preserve area or directions
Good for displaying information across oceans
Major distortion at poles and edges
Land area is small and limited for displaying
information
MODERN MAP
TECHNOLOGY
There are a number of tools that cartographers use to gather data to display on maps.
Some methods are decidedly more high tech, and others are more traditional.
MODERN MAP
TECHNOLOGY
High Tech Methods
High Tech methods tend to rely
on computers in some way,
shape or form.
Rather than by hand,
cartographers use computers
both to gather data and to
create maps.
MODERN MAP
TECHNOLOGY
Global Positioning
System
(GPS)
Remote
Sensing
Geographic
Information
System
(GIS)
MODERN MAP
TECHNOLOGY
Going Old School
It’s important to remember the less
high tech, more first person methods of
gathering map data:
Census: a complete, official
enumeration of a population’s
characteristics
Polls and surveys: scientific questioning
of a portion of the population used to
determine larger trends
Field observation: taking data by hand
by observing it on location