CS 128/ES 228 - Lecture 2a 1
What are maps & what are they used for?
CS 128/ES 228 - Lecture 2a 2
Early mental maps are egocentric
CS 128/ES 228 - Lecture 2a 3
Where would you like to live?
CS 128/ES 228 - Lecture 2a 4
The geocentric map concept
Based on: four cardinal
directions
angles and distances
Directions to campus1. It is easiest to approach campus from Route 17
(now called I-86). Take exit 24 (marked "Allegany - St. Bonaventure University"). At the end of the ramp, turn south (left if coming from Rt. 17 West, right if from Rt. 17 East). Drive about 1/2 mile to a "tee".
2. At the tee, turn left onto Route 417. Drive just over 2 miles, through the village of Allegany and across a high bridge over railroad tracks. Campus is visible to the right.
3. Immediately at the end of the bridge take the first right onto College Road (if you get to the traffic light, you've gone slightly too far. Turn around and return to College Road). Take the second left into a the parking lot marked at the bottom of the map.
CS 128/ES 228 - Lecture 2a 5
What is a map?
“Art is a lie which makes us realize the truth.” P. Picasso
“So is a map.” P. Muehrcke (Map Use. 2nd ed. 1986)
“A map is a spatial model, an attempt to depict selected aspects of a portion of Earth’s surface on a flat plane.” T. Georgian
CS 128/ES 228 - Lecture 2a 6
Warning!!!
“Map and reality are not, cannot be identical.
No aspect of map use is so obvious yet so often
overlooked. Most map reading mistakes occur
because the user forgets this vital fact and
expects a one-to-one correspondence between
map and reality.”
P. Muehrcke Map Use (p. 19)
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How does a map differ from reality? Size
Dimensionality
Amount of detail
Symbolic presentation
Static vs. dynamic
???
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What about aerial photographs?
Aren’t they realistic?
CS 128/ES 228 - Lecture 2a 9
Cartography: the art & science of creating maps
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4 steps of cartography:
1. Selection
2. Simplification
3. Exaggeration
4. Symbolization
See textbook, Box 2.3 (p. 27) for a different list
CS 128/ES 228 - Lecture 2a 11
1. Selection
Depends on: Purpose
Data availability
Size and scale of map
CS 128/ES 228 - Lecture 2a 12
Selection: scale
One of the most important choices – determines what can or cannot be included in the map
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Representing a map’s scale
Scale ratio ex. 1:24,000
Verbal scale ex. 1 inch equals 2000 feet (often used with mixed units)
Coverage ex. 7 ½ minute topographic quadrangle
Scale line ex.
CS 128/ES 228 - Lecture 2a 14
Large and small scales
Large scale: Scale ratio is a
large fraction a given feature
looks large
Small scale: Scale ratio is a
small fraction a given feature
looks small
CS 128/ES 228 - Lecture 2a 15
The dilemma of scale
Small scale maps lack detail
Large scale maps lack range (coverage)
The dilemma can be alleviated somewhat by: - locator maps--
- inset maps
CS 128/ES 228 - Lecture 2a 16
Inset maps
User must dealwith multiplescales
Rule: the insetalways ends justshort of the point of interest
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Selection: coverage
State maps minimize details in adjacent states
Topographic maps omit detail in urban areas
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Selection: time frame
Maps are essentially snapshots
Two rules:
1. Every map should be dated!!
2. Don’t trust the dates
CS 128/ES 228 - Lecture 2a 19
2. Simplification
Begins with choice of scale
Other issues: Reduced dimensionality of line or area features Smoothing lines and boundaries Aggregation
CS 128/ES 228 - Lecture 2a 20
Reduced dimensionality
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Smoothing lines and boundaries
The blues lines are from a digitized U.S.G.S. 7 ½ min topographic map. Note how the channel of Fourmile Creek been smoothed.
CS 128/ES 228 - Lecture 2a 22
Aggregation
Like smoothing, but refers to scale of spacing of objects
Depends not only on scale but also on purpose of map
CS 128/ES 228 - Lecture 2a 23
3. Exaggeration
Why, given scale limitations, would map makers make features or labels larger?
Make symbols visible
Separate features and symbols
CS 128/ES 228 - Lecture 2a 24
4. Symbolization
1. Size, texture, and density
CS 128/ES 228 - Lecture 2a 25
Issues of Symbolization
1. Size, texture, and density
CS 128/ES 228 - Lecture 2a 26
Issues of Symbolization
1. Size, texture, and density
http://www.atsdr.cdc.gov/HEC/HSPH/v5n21.jpg
http://www.clarelibrary.ie/eolas/coclare/places/major_towns.htm
CS 128/ES 228 - Lecture 2a 27
Issues of Symbolization
2. Use of color
CS 128/ES 228 - Lecture 2a 28
Issues of Symbolization
3. Realistic vs. abstract
CS 128/ES 228 - Lecture 2a 29
Symbolization
Find here decisions about:
Size, texture, and density
Use of color
Realistic vs. abstract symbols