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GIS Roots in Cartography

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

Basic Cartographic Principles

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

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.

Cartography

- The art, science, and craft of mapmaking.
- Cartography is the science that deals with the

construction, use, and principles behind maps.

Quote from Edwin Raisz

GIS Data Linked with Maps

Data

- a set of measurements, text, or other values for

at least one attribute and at least one record.

Database

- a collection of data organized in a systematic

way to provide access on demand.

File

- data logically stored together at one location on

the storage mechanism of a computer (e.g. on

disk).

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.

Values

- the content of an attribute for a single record

within a database. Values can be text, numeric,

or codes.

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.

Attributes

- Attributes
- Parcel number
- Owner
- Address
- Value

- Graphic (map) feature
- Parcels

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?

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.

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

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.

Geoid Measurements

The Spheroid and Ellipsoid

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.

Earth Models and Datums

The Datum

- An ellipsoid gives the base elevation for

mapping, called a datum. - Relative to geographic area being projected
- Examples are NAD27 and NAD83.

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.

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.

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.

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.

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.

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.

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.

General Maps

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

Thematic Maps

- Choropleth Portrayal of a statistical surface

by areal symbols. - Dot maps
- Proportional symbol maps
- Isometric (e.g. contour) maps

Charts

- Navigation Charts
- Aeronautical
- Nautical
- Bathymetric

Map Design Components

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

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

Cartographic Generalization

- Simplification
- Classification
- Symbolization
- Induction

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.

Classification

- The ordering or scaling and grouping of data.

Symbolization

- The graphic encoding of the scaled and/or grouped

essential characteristics, comparative

significance, and relative positions.

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.

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

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

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

Discrete Data

These data are discrete. There is empty space

between buildings and pipelines.

Continuous Data

This image depicts elevation bands. There is

elevation everywhere.

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

Map Types Point Data

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

Map Types Line Data

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

Map Types Area Data

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

Map Types Volume Data

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

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)

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

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

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

Break

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.

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.

Scale of a baseball earth

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

Small vs. Large Scale Maps

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

Presentations of Map Scale

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

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.

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!

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

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

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

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

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.

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.

Coordinate Systems

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

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.

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.

X and Y Confusion

- Question Which values represent the X and Y

coordinates in latitude and longitude?

Latitude/Longitude

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

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.

UTM Zones in theContinental U.S.

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

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.

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

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.

Colorado State Plane Zones

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

GIS Capabilities

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

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.

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.