GEOGRAPHIC INFORMATION SYSTEMS
Lecture 03: Introduction to Maps
Introduction to Maps
What is a map?
- simple definition: a map is a scale model of the surface of the earth
- like all scale models, a map is an abstracted and generalized version of reality
- abstraction: only selected features (layers) are displayed, can’t show every feature in the real world
- generalization: features are simplified, can’t show all of the detail associated with real-world features
Basic Characteristics
- all maps are concerned with location
- location of features defined by points, lines, polygons – or surface values
- all maps are scaled reductions of reality
- the map scale defines the relationship between the map and reality
- all maps involve transformations of reality
- map projections are used to represent a spherical surface of the Earth on a flat map
- all maps involve some abstraction of reality
- can't show every feature in the real world – only selected layers are displayed
- level of abstraction depends upon: 1) the purpose of the map and 2) the map scale
- all maps involve some generalization of reality
- features are simplified (e.g. cities are represented by points, roads are represented by simple lines)
- level of generalization depends upon: 1) the purpose of the map and 2) the map scale
- all maps use symbology to represent features
- features are symbolized by varying size, colors, tones, patterns, or using specialized symbols
Map Scale
- given that a map is a scale model of the surface of the earth …
- the map scale tells a map reader the scale at which the earth's surface is being represented
- there are three main types of map scale (know the advantages and disadvantages of using each type)
1) verbal scale:
easy to understand
difficult to convert units
not valid if map is enlarged or reduced
2) bar scale:
easy to understand
remains valid if map is enlarged or reduced
difficult to convert units
3) representative fraction (ratio):
not dependent on measurement units
difficult to visualize
not valid if map is enlarged or reduced
- to overcome the limitations associated with a single type of map scale, the USGS uses four different types
of map scales on a standard topographic map. These four map scales are:
1) the representative fraction, 2) a bar scale in miles, 3) a bar scale in feet and 4) a bar scale in kilometers
Copyright © Kevin Mulligan, Texas Tech University
Types of Maps
- maps are categorized by their 1) scale and 2) function (e.g. a small scale, quantitative thematic map)
1) Maps Categorized by Scale
- we often use the terms “large scale“ and “small scale” to describe maps
- these are relative terms on a continuum of scales (some examples below)
1:10,000,000
very small scale
- a country
1:1,000,000
small scale
- a state
1:250,000
medium scale
- county
1:24,000
large scale
- topo map
1:5000
very large scale
- a neighborhood
- do not be confused on this…
- for example, a world map is a very small scale maps (even though it covers the whole world)
- this is because 1/35,000,000 is a much smaller number (fraction) than 1/5,000
- an easy way to remember is:
- large scale maps have large features
- small scale maps have small features
- comparing large scale vs small scale maps, be familiar with the following properties:
Large Scale (1:5,000)
Small Scale (1:1,000,000)
- area covered
small area
large area
- level of abstraction
less abstract
more abstract
- level of generalization
less generalized
more generalized
- projection
less important
more important
- errors associated with datum
more important
less important
2) Maps Categorized by Function
- general reference maps
- road maps, topographic maps, etc
- cadastral maps or plat maps
- property boundaries (polygons) - derived from a cadastral survey
- charts
- maps used for navigation (nautical or aeronautical charts)
- qualitative thematic maps
- categories of non-numerical data (e.g. soils, vegetation, land use)
- quantitative thematic maps
- classification of numerical data (e.g. bank assets, pop density)
Copyright © Kevin Mulligan, Texas Tech University
GIST 3300 / 5300
Geographic Information Systems
Introduction to Maps
What is a map?
- a simple definition
Basic Characteristics
- location, scale, transformations, abstraction, generalization, symbology
Map Scales
- verbal scales, bar scales and the representative fraction
Types of maps
- small scale vs large scale maps
- maps classified by their function
Geographic Information Systems
What is a map?
Simple definition:
- a map is a scale model of the surface of the earth
SCALE = 1:35,000,000
Geographic Information Systems
What is a map?
Like all scale models…
- a map is an abstracted and generalized version of reality
- abstraction
- can’t show everything in the real world
- only selected layers are displayed
- generalization
- can’t show all of the detail associated with real world features
- features in a layer must be simplified (generalized)
All maps are abstractions of reality and the features are generalized.
Geographic Information Systems
What is a map?
Abstraction
- only selected layers
are displayed
Generalization
- features are simplified
Geographic Information Systems
What is a map?
- abstraction and generalization
Geographic Information Systems
Basic Characteristics of Maps
1) all maps are concerned with location
- location of features defined by points, lines, polygons
- location of surface values
2) all maps are scaled reductions of reality
- map scale - relationship between map and reality
3) all maps involve transformations of reality
- map projections – mathematical transformation used to
represent a spherical surface on a flat map
4) all maps involve some abstraction of reality
- can't show every feature in the real world
- level of abstraction depends upon:
1) the purpose of the map
2) the map scale
Geographic Information Systems
Basic Characteristics of Maps
5) all maps involve some generalization of reality
- features are simplified
e.g. vegetation types are generalized
e.g. roads are represented by a simple line
e.g. cities are represented by a single point or polygon
- level of generalization depends upon:
1) the purpose of the map
2) the map scale
6) all maps use symbology to represent features
- point symbols (size, color, specialized symbols)
- line symbols (thickness, color, dashed, specialized symbols)
- polygons (color, tone, pattern, specialized symbols)
- surfaces (color, tone, shading, pattern)
Geographic Information Systems
Map Scale
- if a map is a scale model of the surface of the Earth
- the map scale tells a reader the scale at which the Earth's surface
is being represented
Types of Map Scale
- there are three main types of map scale
1) verbal scale
2) bar scale
3) representative fraction
Geographic Information Systems
Verbal Scale
Example
One inch = 2,000 feet
Advantage
- easy to understand
Disadvantage
- difficult to convert measurement units
- not valid if the map is enlarged or reduced
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Bar Scale
Example
0
50
100 Miles
Advantage
- easy to understand
- remains valid if map is enlarged or reduced
Disadvantage
- difficult to convert measurement units
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Representative Fraction
Example
1:24,000
1/24,000 (ratio)
Advantage
- not dependent upon measurement units
Disadvantage
- difficult to visualize
- not valid if the map is enlarged or reduced
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U.S.G.S. Topographic Map
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Map Scale
Selecting a Scale Bar in ArcMap
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Map Scale
Selecting a Representative Fraction or Verbal Scale in ArcMap
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Types of Maps
- maps are usually categorized by their scale and function
for example: a small scale, quantitative thematic map
United States
Population Density
Geographic Information Systems
Types of Maps
Maps Categorized by Scale
- large scale vs small scale maps
- relative terms (on a continuum of map scales)
1:10,000,000
very small scale
(country)
1:1,000,000
small scale
1:250,000
1:24,000
1:5,000
medium scale
large scale
very large scale
(topo map)
(neighborhood)
(state)
Small scale map = small features
(county)
Large scale map = large features
Geographic Information Systems
Types of Maps
Maps Categorized by Scale
- comparing basic properties
1:5,000
large scale map
1:1,000,000
small scale map
Area Covered
small area
large area
Abstraction
less abstract
more abstract
(more feature types)
(fewer feature types)
less generalized
more generalized
(more feature detail)
(less feature detail)
Projection
less important
very important
Datum
very important
less important
Generalization
Geographic Information Systems
Types of Maps
Maps Categorized by Function
- general reference
- road maps, topographic maps, etc
- cadastral maps (plat maps)
- property boundaries (derived from a cadastral survey)
- charts
- maps used for navigation (nautical or aeronautical charts)
- qualitative thematic maps
- categories of non-numerical data
e.g. soils, vegetation, landforms
- quantitative thematic maps
- classification of numerical data
Geographic Information Systems
General Reference – Road Map
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General Reference – U.S.G.S. Topographic Map
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Cadastral or Plat Map
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Charts - Aeronautical Chart
Operational Navigation Chart (ONC)
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Charts - Nautical Chart
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Qualitative Thematic Map
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Quantitative Thematic Map
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