GIS Roots in Cartography

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GIS Roots in Cartography

• Front Range Community College
• GIS 101 Week 2
• Damon D. Judd

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Basic Cartographic Principles

• Principles of Geodesy and Cartography
• Measuring the Earth
• Characteristics of Geographic Data
• Map Scale Map Projections
• Coordinate Systems
• Maps and Attributes

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Cartography and GIS

• Understanding the way maps are encoded to be used
  in GIS requires knowledge of cartography.
• Cartography is the science that deals with the
  construction, use, and principles behind maps.
• A map is a depiction of all or part of the earth
  or other geographic phenomenon as a set of
  symbols and at a scale whose representative
  fraction is less than one to one.

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Cartography

• The art, science, and craft of mapmaking.
• Cartography is the science that deals with the
  construction, use, and principles behind maps.

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Quote from Edwin Raisz
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GIS Data Linked with Maps
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Data

• a set of measurements, text, or other values for
  at least one attribute and at least one record.

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Database

• a collection of data organized in a systematic
  way to provide access on demand.

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File

• data logically stored together at one location on
  the storage mechanism of a computer (e.g. on
  disk).

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Record

• a set of values for all attributes for a given
  feature or object stored in a database.
  Equivalent to a row of a data table.

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Values

• the content of an attribute for a single record
  within a database. Values can be text, numeric,
  or codes.

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Attribute

• A numerical entry that reflects a measurement or
  value for a feature.
• Attributes can be labels, categories, or numbers
  they can be dates, standardized values, or fields
  or other measure items.
• An item for which data are collected and
  organized. A column in a table or data file.

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Attributes

• Attributes
• Parcel number
• Owner
• Address
• Value

• Graphic (map) feature
• Parcels

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Mapping the Earth

• How big is the earth?
• What is a map?
• How is map data stored in a computer for use with
  a GIS?
• Why is the way we store digital data about the
  Earth important?

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Geodesy

• The science which deals with the determination of
  the size and shape of the Earth, and which
  derives three-dimensional positions for points
  above, on, and below the surface of the Earth.

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How Big is the Earth?

• Nearly 25,000 miles (40 million meters) in
  circumference.
• The earth can be modeled as a
• sphere
• oblate ellipsoid
• geoid

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The Geoid

• The geoid is the surface of reference for
  astronomic observations and for geodetic
  leveling.
• The geoid is a figure that adjusts the best
  ellipsoid and the variation of gravity locally.
• It is the most accurate, but is not typically
  used for GIS and cartography.

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Geoid Measurements
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The Spheroid and Ellipsoid
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Oblate Ellipsoid

• An oblate ellipsoid is an ellipse rotated in
  three dimensions about its shorter axis.
• The earth's ellipsoid is only 1/297 off from a
  sphere.
• Many ellipsoids have been measured, and maps
  based on each. Examples are WGS84 and GRS80.

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Earth Models and Datums
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The Datum

• An ellipsoid gives the base elevation for
  mapping, called a datum.
• Relative to geographic area being projected
• Examples are NAD27 and NAD83.

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NAD 27

• North American Datum of 1927.
• Used on older mapping. Datum origin centered on
  Meades Ranch, Kansas.
• Many older maps still use NAD 27.

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NAD 83

• North American Datum of 1983
• The horizontal control datum for the United
  States, Canada, Mexico, and Central America.
• Based on a geocentric origin and Geodetic
  Reference System 1980 (GRS80).
• The basis for all maps created since 1986 - a
  small percentage of the total.

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World Geodetic System 1984 (WGS84)

• Revised in 1984 from GRS80.
• A unified world datum based on a combination of
  all available astrogeodetic, gravimetric, and
  satellite tracking observations.
• The reference ellipsoid is revised as new
  measurement techniques change the currently
  accepted values.
• A common datum used in GPS receivers.

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Definition Map

• A representation usually on a flat surface of
  the whole or part of an area.
• The graphic representation of spatial
  relationships and spatial forms.
• A graphic depiction of all or part of a
  geographic realm in which the real-world features
  have been replaced by symbols in their correct
  spatial location at a reduced scale.

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The Scope of Cartography

• The Cartographer and the Map User.
• Ask yourself Who is the audience of the map
  presentation?
• The cartographic sequence is the cycle of events
  that occur in map making and map reading.

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The Cartographic Sequence

• Collecting and selecting the data for mapping.
• Manipulating and generalizing the data, designing
  and constructing the map.
• Reading or viewing the map.
• Responding to or interpreting the data.

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Functional Types of Maps

• General Portray the spatial association of
  selected geographical phenomena.
• Thematic Concentrate on the spatial variations
  of the form of a single attribute or the
  relationship among several attributes.
• Charts Serve the needs of navigators.

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General Maps

• Road/Planimetric
• Topographic
• Atlas
• Cadastral/Property Map
• Facility/Engineering
• Site Plan/Map
• Orthophoto Map
• Lunar/Planetary

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Thematic Maps

• Choropleth Portrayal of a statistical surface
  by areal symbols.
• Dot maps
• Proportional symbol maps
• Isometric (e.g. contour) maps

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Charts

• Navigation Charts
• Aeronautical
• Nautical
• Bathymetric

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Map Design Components

• Every map should have
• Title
• Legend
• Map scale
• North arrow
• Credits
• Date

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Categories of Map Features

• Consider classifying or organizing map features
  by type.
• Examples of map feature types
• Planimetry
• Topography
• Cadastral
• Areas/Political Boundaries
• Facilities
• Natural Resources

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Cartographic Generalization

• Simplification
• Classification
• Symbolization
• Induction

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Simplification

• The determination of the important
  characteristics of the data, the elimination of
  unwanted detail, and the retention and possible
  exaggeration of the important characteristics.

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Classification

• The ordering or scaling and grouping of data.

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Symbolization

• The graphic encoding of the scaled and/or grouped
  essential characteristics, comparative
  significance, and relative positions.

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Induction (Interpolation)

• The application of the logical process of
  inference.
• Creating a soil type map with sample point data.
• Creating a DEM from elevation points.

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Choosing the Wrong Map Type

• Fairly common GIS error.
• Often due to lack of knowledge about cartographic
  options.
• Can still have perfect symbolization.
• Possibility of misinformation (e.g. wrong data
  values).
• Definite reduction in communication
  effectiveness.
• Ref How to Make Maps Lie, by Mark Monmonier

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Choosing Types

• Check the data
• Continuous
• Discrete
• Accuracy Precision
• Reliability
• Dimension (Point, Line, Area, Volume)
• Scale of Measurment (NOIR)
• GIS capability
• May need to supplement GIS software

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Continuity of Geographic Data

• Discrete Distributions - Discrete data have known
  and definable boundaries.
• distinct separation between objects
• houses, city boundaries, roads
• best represented using the vector data model
• Continuous Distributions - do not have distinct
  boundaries like discrete geographic features.
• no empty space
• elevation, precipitation, reflectance
• best represented with raster data model

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Discrete Data
These data are discrete. There is empty space
between buildings and pipelines.
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Continuous Data
This image depicts elevation bands. There is
elevation everywhere.
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Classes of Geographic Phenomena - Dimensionality

• Positional
• point in space well, pole
• Linear data
• one-dimensional data road network
• Area/Polygon data
• two dimensional data city boundary
• Volumetric data
• 3-D volume of contaminated soil

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Map Types Point Data

• Reference (e.g. City on small-scale map)
• Topographic
• Dot
• Picture Symbol
• Graduated Symbol

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Map Types Line Data

• Network
• Flow
• Isopleth
• Reference (e.g. County Boundary)

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Map Types Area Data

• Choropleth
• Area qualitative
• Stepped surface
• Hypsometric (e.g. elevation ranges)
• Dasymetric
• Reference

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Map Types Volume Data

• Gridded fishnet
• Realistic perspective
• Hill-shaded
• Image map
• Subsurface volumetrics

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Data Scaling

• Nominal (Name of a place)
• Ordinal (Small, medium, large town)
• Interval (Arbitrary zero e.g. Sea Level)
• Ratio (Absolute zero e.g. population, densities)

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Nominal

• Distinguish between objects based on their
  intrinsic character qualitative differentiation.
• Root of word nominal is nom, or name.
• point wholesale vs. retail establishment
• line river vs. road
• area land use class, e.g., urban vs. rural

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Ordinal

• Involves nominal classification, but also
  differentiates within a class of data involves
  rank of objects, but NOT a measurement.
• point classification of cities into small,
  medium, and large
• line large river vs. small river vs. creek, or
  major highway vs. secondary roads
• area crop yield high, medium, low

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Interval/Ratio

• Adds information of distance between ranks to the
  description of class and rank uses standard
  units and then expresses the difference in terms
  of standard unit. Interval can be an arbitrary
  scale Ratio uses an absolute value from a datum.
  
• point spot elevation or precipitation values
• line contour lines
• area average temperature of a state number of
  species within an eco-region

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Break
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Making Maps of the Earth

• Map Scale - The ratio of distance measured on a
  map to the corresponding distance on the ground.
• Map Projections - A mathematical model used to
  transform positions on the curved surface of the
  earth onto a flat map surface.
• Coordinate Systems - a standardized method for
  assigning codes to locations so that locations
  can be found using the codes alone.

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Map Scale

• Map scale is based on the representative
  fraction, the ratio of a distance on the map to
  the same distance on the ground.
• A GIS is scaleless because maps can be enlarged
  and reduced and plotted at many scales other than
  that of the original data.
• To compare or edge-match maps in a GIS, both maps
  MUST be at the same scale and have the same map
  extent.

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Scale of a baseball earth

• Baseball circumference 226 mm
• Earth circumference approx 40 million meters
• RF is 1177 million

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Small vs. Large Scale Maps

• Small scale
• Covers large area
• Less detail
• Large scale
• Covers small area
• Greater detail

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Presentations of Map Scale

• Bar scale
• Example 0__________100mi.
• Verbal or Engineering scale
• Example 1100
• Representative Fraction
• Example 124,000

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Map Projections

• A mathematical model used to transform positions
  of the spherical or ellipsoidal earth onto a flat
  map surface.
• The map projection can be onto a flat surface or
  a surface that can be made flat by cutting, such
  as a cylinder or a cone.
• If the globe, after scaling, cuts the surface,
  the projection is called secant. Lines where the
  cuts take place or where the surface touches the
  globe have no projection distortion.

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Properties of Map Projections

• Projections can be based on axes parallel to the
  earth's rotation axis (equatorial), at 90 degrees
  to it (transverse), or at any other angle
  (oblique).
• A projection that preserves the shape of features
  across the map is called conformal.
• A projection that preserves the area of a feature
  across the map is called equal area or
  equivalent.
• No flat map can be both equivalent and conformal!

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Mercator Projection

• Used for navigation or maps of equatorial regions
  (1569)
• Distance only true along equator
• Area distortion increases away from equator
• Conformal in angles and shapes in small areas
• Latitude longitude straight lines

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Albers Equal Area

• Conic
• Used by USGS for conterminous US
• All areas proportional to same area on the Earth
• Directions are reasonably accurate in limited
  regions
• Distances true on standard parallels

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Lambert Conformal Conic

• Used by USGS for State Base Map Series
• Looks like Albers Equal Area
• Distance true along standard parallels
• Directions reasonably accurate
• Shapes essentially true

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Azimuthal Equidistant

• Used by USGS in National Atlas of the United
  States of America
• Distances and directions true to all points from
  center point of projection
• Distortion increases away from center point

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Map Projection References

• Pearson, Frederick. Map Projections Theory and
  Applications. Boca Raton CRC Press, Inc., 1990
• Robinson, Arthur et. al. Elements of
  Cartography. New York John Wiley Sons, Inc.,
  1995.
• Snyder, John P. Map Projections - A Working
  Manual. U.S. Geological Survey Professional
  Paper 1395. Washington United States
  Government Printing Office, 1987.

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Coordinate Systems - definition

• A coordinate system is a standardized method for
  assigning codes to locations so that locations
  can be found using the codes alone.
• Standardized coordinate systems use absolute
  locations.
• In a Cartesian coordinate system, the x-direction
  value is the easting and the y-direction value is
  the northing. Most systems make both values
  positive.

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Coordinate Systems

• Geographical Coordinates or Spherical Coordinates
• Example Latitude/Longitude
• Plane Rectangular or Cartesian Coordinates
• Universal Transverse Mercator (UTM)
• State Plane Coordinate System

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Latitude/Longitude

• Equator 0
• North Pole 90
• South Pole 90
• Prime Meridian 0
• Intl Date Line 180
• Latitude Parallels
• Longitude Meridians
• In GIS software we use negative values in West
  and South quadrants.

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Coordinate Systems for the US

• Some standard coordinate systems used in the
  United States are
• geographic coordinates
• Universal Transverse Mercator (UTM)
• State Plane
• To compare or edge-match maps in a GIS, both maps
  MUST be in the same coordinate system.

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X and Y Confusion

• Question Which values represent the X and Y
  coordinates in latitude and longitude?

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Latitude/Longitude

• Expressed in Degrees, Minutes, Seconds (DMS)
• or
• Expressed in Decimal Degrees (DD)
• For example, 40 30 can be expressed as 40.5

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Universal Transverse Mercator (UTM) Coordinates

• A common rectangular (Cartesian) coordinate
  system based on projection of a location on the
  earth onto a cylindrical surface.
• Coordinates are usually expressed in meters north
  (northings) and meters east (eastings) from
  reference axes that define a given zone.

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UTM Zones in theContinental U.S.
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Denver

• Approximate Latitude / Longitude
• 40 degrees north latitude
• 105 degrees west longitude (-105)
• UTM Zone 13
• Easting 500,000m E
• Northing 4,000,000m N

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State Plane Coordinate System

• A grid system that was developed by the National
  Geodetic Survey for each state.
• The earths surface, reduced to sea level, is
  projected onto a series of planar surfaces.
• A Lambert conical or Transverse Mercator
  projection is used, depending on the states
  shape.
• A state can have more than one zone, and each
  zone has an origin for a grid system.

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State Plane Coordinates (cont.)

• The location of points is expressed in terms of
  coordinates x and y from this origin.
• Based on Transverse Mercator or Lamberts Conic
  Projections
• Feet (can be translated to meters)
• Large states broken into zones
• Colorado North, Central, South

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1997 Colorado Revised Statutes

• 38-52-101. Colorado coordinate system zones
  defined.
• (1) The systems of plane coordinates which have
  been established by the national ocean
  service/national geodetic survey (formerly the
  United States coast and geodetic survey) or its
  successors for defining and stating the
  geographic positions or locations of points on
  the surface of the earth within the state of
  Colorado are, on and after July 1, 1988, to be
  known and designated as the Colorado coordinate
  system of 1927 and the Colorado coordinate system
  of 1983. (2) For the purpose of the use of these
  systems, the state is divided into a north zone,
  a central zone, and a south zone. (3) The area
  now included in the following counties shall
  constitute the north zone Moffat, Routt,
  Jackson, Larimer, Weld, Logan, Sedgwick, Rio
  Blanco, Grand, Boulder, Gilpin, Adams, Morgan,
  Washington, Phillips, and Yuma. (4) The area now
  included in the following counties shall
  constitute the central zone Garfield, Eagle,
  Summit, Clear Creek, Jefferson, Denver, Arapahoe,
  Lincoln, Kit Carson, Mesa, Delta, Pitkin,
  Gunnison, Lake, Chaffee, Park, Fremont, Teller,
  Douglas, El Paso, Elbert, and Cheyenne. (5) The
  area now included in the following counties shall
  constitute the south zone Montrose, Ouray,
  Hinsdale, Saguache, Custer, Pueblo, Crowley,
  Kiowa, San Miguel, San Juan, Mineral, Rio Grande,
  Alamosa, Huerfano, Otero, Bent, Prowers, Dolores,
  Montezuma, La Plata, Archuleta, Conejos,
  Costilla, Las Animas, and Baca.

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Colorado State Plane Zones
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University of Denver GIS Lab

• Lat/Long (DMS)
• 39 40 28.29738 N.
• 104 57 47.70038 W.
• State Plane Coordinates
• 2,151,089 feet East
• 671,008 feet North
• UTM
• 503,151 meters East,
• 4,391,634 meters North

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GIS Capabilities

• A GIS package should be able to move between
• map projections,
• coordinate systems,
• datums, and
• ellipsoids.

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Coordinate Transformation

• The ability to translate or transform different
  coordinate systems into the coordinate system of
  choice.
• Provides capability to merge data from disparate
  sources into common coordinate system framework.

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Summary

• GIS has its roots in cartography. The ability to
  make maps on the computer has been around since
  the 1950s.
• With the linking of a database to a map, we truly
  have a Geographic Information System.
• Projections and coordinate systems are a way of
  organizing data describing a spherical
  (elliptical) planet onto a flat surface.