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 conceptBased 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 geographic region 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 equivalent

to reality?


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

For my part of this course, learn

outlines!!


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 (Where’s SBU?)


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 scalesLarge 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

Great invention, but:


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. SimplificationBegins 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. ExaggerationWhy, given scale

limitations, would map makers make features or labels larger?

Make symbols visible

Separate features and symbols


3. ExaggerationExaggeration also reflects

a map’s purpose

Saul Steinberg’s Mar. 29, 1976 cover of the New Yorker

magazinehttp://www.totalmedia.com/images/Newyorker.jpg


4. Symbolization1. Size, texture,

and density


Issues of Symbolization1. Size, texture,

and density

Which symbols are emphasized on this map? Why?


Issues of Symbolization1. Size, texture,

and density

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

http://blogjunky.blogspot.com/populationmap.gif


Issues of Symbolization2. Use of color


Issues of Symbolization3. Realistic vs. abstract


SymbolizationWhat decisions does

this map reveal about:

Size, texture, and density

Use of color

Realistic vs. abstract symbols

what are maps & what are they used for?

Documents

scale of map cs

purpose of map cs

small cs

maps scale scale ratio

lecture 2a14large

lecture 2a13representing

lecture 2a18selection

lecture 2a8what