Introduction to Cartography

1
Introduction to Cartography

• Map - a representation, normally to scale and on
  a flat medium, of a selection of material or
  abstract features on, or in relation to, the
  surface of the Earth (International Cartography
  Association)

2
Cartographic Abstraction

• The production of a map requires
• selection of the few features in the real world
  to include
• classification of selected features into groups,
  (e.g., bridges, churches, railways)
• simplification, e.g., of jagged lines like
  coastlines
• exaggeration of features to be included that are
  too small to show at the scale of the map
• symbolization to represent the different classes
  of features chosen

3
Selection

• Selecting a region, time frame
• Selecting variables to be mapped
• Selecting a scale
• Measurement level
• nominal
• ordinal
• interval
• ratio

4
Scale

• Scale ratio between distances on the map and
  the corresponding distances in the real world.
  Terms can be confusing
• A large scale map shows great detail and small
  features, fraction is large, e.g., 1/10,000
• A small scale map shows only large features,
  fraction is small, e.g., 1/1,000,000
• Scale influences how features are shown, and
  which features are shown
• One inch one mile is a scale of 1/____?

5
Levels of measurement

• Nominal (categorical)
• classes, assumed to be similar within classes and
  dissimilar between classes
• no ranking implied, just names of class
• if just two categories, also called binary
• Ordinal
• implicit ranking, e.g., high, medium, low
• nothing implied about intervals between classes

6
Levels of measurement (cont.)

• Interval
• numbers are used, and intervals between groups
  have meaning
• numbers not absolute (e.g., temperature)
• Ratio
• numbers have absolute meaning, a true zero is
  established

7
Classification

• Classification of features into groups
• Also, classification of values into groups
• Number of classes
• Class limits
• constant intervals
• variable intervals

8
Simplification

• Similar to classification, in that it simplifies,
  but it goes further
• Eliminating unwanted features
• Smoothing of detail
• Reducing data measurement levels
• Combining variables into ratios or indices

9
Exaggeration

• Enlarging features too small to be shown at the
  scale of a map
• Making distinctions normally not seen at that
  scale
• Lying to tell the truth - exaggeration in
  symbolization.

10
Symbolization

• Used to represent different features and classes
  of features
• Depends on
• class of geographic data (point, line, area,
  volume)
• measurement level (nominal, ordinal, interval,
  ratio)
• Many options for symbolization
• size, shape, pattern (orientation, arrangement,
  texture), color (hue, intensity)

11
Types of Maps

• Descriptive/reference/topographic maps
• a reference tool, shows outlines of natural and
  man-made features
• topography refers to shape of earth, but
  topographic maps also show roads and other
  features
• Thematic maps
• communicate concepts, convey data

12
Types of Maps

• Thematic maps
• Chloropleth map
• reporting zones, e.g., counties/states,
  established independently of data, may be used to
  convey other data
• Area class map
• zones determined by variation of data, e.g., soil
  type, land cover, vegetation
• Isoline/isopleth/contour map
• lines join points of equal value

13
Projections

• The earth is curved, but on a map it is shown on
  a flat surface.
• A projection is the method by which this is done.
• This creates distortions of one or more map
  properties
• shape
• area
• distance
• direction

14
Projections

• Projection methods
• Conic, Cylindrical, Planar
• Names based on properties preserved
• Conformal projections preserve shape
• Equal area/equivalent projections preserve area
  (useful for applications requiring area, popular
  in GIS)
• Equidistant projections preserve distance to
  places from one or two points

15
Coordinate systems

• Definition - a system with all the necessary
  components to locate a position in two or three
  dimensional space, i.e., an origin, a type of
  unit distance, and two axes

16
State Plane Coordinate (SPC) system

• United States split up into about 130 zones, each
  with its own projection surface
• designed to reduce distortion caused by
  projections over large areas
• distortion error designed to be lt 1 in 10,000
  (for every 10,000 feet, no more than 1 foot off)
• Lambert conformal projection used for east-west
  extent, Transverse Mercator for north-south
• false origin placed at to southwest, coordinates
  in form false easting, false northing (in
  feet)
• e.g., state capitol in Madison, WI is at
  2,164,606 feet E, 392,285 feet N, Wisconsin S.

17
Universal Transverse Mercator (UTM) grid system

• 60 north-south zones, 6 degrees longitude each,
  with 1/2 degree overlap
• each zone further subdivided into zones of 8
  degrees latitude
• separate grid for each zone, 1 in 2500 maximum
  distortion
• false origin at the equator and to the west
  coordinates in form false easting, false
  northing (in meters)
• e.g., state capitol in Madison, WI is at 305,904
  meters E, 4,771,651 meters N, 16, N