CS 128/ES 228 - Lecture 2a1 What are maps & what are they used for?

CS 128/ES 228 - Lecture 2a 1

What are maps & what are they used for?


Early mental maps are egocentric


Where would you like to live?


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.


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


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)


How does a map differ from reality? Size

Dimensionality

Amount of detail

Symbolic presentation

Static vs. dynamic

???


What about aerial photographs?

Aren’t they realistic?


Cartography: the art & science of creating maps


4 steps of cartography:

1. Selection

2. Simplification

3. Exaggeration

4. Symbolization

See textbook, Box 2.3 (p. 27) for a different list


1. Selection

Depends on: Purpose

Data availability

Size and scale of map


Selection: scale

One of the most important choices – determines what can or cannot be included in the map


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.


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


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


Inset maps

User must dealwith multiplescales

Rule: the insetalways ends justshort of the point of interest


Selection: coverage

State maps minimize details in adjacent states

Topographic maps omit detail in urban areas


Selection: time frame

Maps are essentially snapshots

Two rules:

1. Every map should be dated!!

2. Don’t trust the dates


2. Simplification

Begins with choice of scale

Other issues: Reduced dimensionality of line or area features Smoothing lines and boundaries Aggregation


Reduced dimensionality


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.


Aggregation

Like smoothing, but refers to scale of spacing of objects

Depends not only on scale but also on purpose of map


3. Exaggeration

Why, given scale limitations, would map makers make features or labels larger?

Make symbols visible

Separate features and symbols


4. Symbolization

1. Size, texture, and density


Issues of Symbolization





http://www.atsdr.cdc.gov/HEC/HSPH/v5n21.jpg

http://www.clarelibrary.ie/eolas/coclare/places/major_towns.htm



2. Use of color



3. Realistic vs. abstract


Symbolization

Find here decisions about:

Size, texture, and density

Use of color

Realistic vs. abstract symbols

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CS 128/ES 228 - Lecture 2a1 What are maps & what are they used for?