What are maps what are they used for

What are maps & what are they used for? CS 128/ES 228 - Lecture 2 a 1

Early mental maps are egocentric CS 128/ES 228 - Lecture 2 a 2

Where would you like to live? CS 128/ES 228 - Lecture 2 a 3

The geocentric map concept Based on: n four cardinal directions n angles and distances Directions to campus 1. 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 2 a 4

What is a map? n “Art is a lie which makes us realize the truth. ” P. Picasso n “So is a map. ” P. Muehrcke (Map Use. 2 nd 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 n CS 128/ES 228 - Lecture 2 a 5

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 (p. 19) CS 128/ES 228 - Lecture 2 a 6

How does a map differ from reality? n Size n Dimensionality n Amount of detail n Symbolic presentation n Static vs. dynamic n ? ? ? CS 128/ES 228 - Lecture 2 a 7

What about aerial photographs? Aren’t they realistic? n n CS 128/ES 228 - Lecture 2 a 8

Cartography: the art & science of creating maps CS 128/ES 228 - Lecture 2 a 9

5 steps of cartography: 1. Selection 4. Exaggeration 2. Classification 5. Symbolization 3. Simplification See textbook, Box 2. 3 (p. 26) for a different list CS 128/ES 228 - Lecture 2 a 10

1. Selection Depends on: n Data availability n Size and scale of map n Purpose CS 128/ES 228 - Lecture 2 a 11

Selection: scale n One of the most important choices – determines what can or cannot be included in the map CS 128/ES 228 - Lecture 2 a 12

Representing a map’s scale § Scale line n Scale ratio 1: 24, 000 n Coverage 7 ½ minute topographic quadrangle CS 128/ES 228 - Lecture 2 a 13

Large and small scales n Large scale: a given feature looks large n Small scale: a given feature looks small CS 128/ES 228 - Lecture 2 a 14

The dilemma of scale n Small scale maps lack detail Large scale maps lack range (coverage) n The dilemma can be alleviated somewhat by: - inset maps - locator maps -- CS 128/ES 228 - Lecture 2 a 15

Inset maps n User must deal with multiple scales n Rule: the inset always ends just short of the point of interest CS 128/ES 228 - Lecture 2 a 16

Selection: coverage n State maps minimize details in adjacent states n Topographic maps omit detail in urban areas CS 128/ES 228 - Lecture 2 a 17

Selection: time frame n Maps are essentially snapshots n Two rules: 1. Every map should be dated!! 2. Don’t trust the dates CS 128/ES 228 - Lecture 2 a 18

2. Classification n Continuous vs. discrete features n There are many ways to represent continuous features on a map n Beware of the boundaries – they’re not real CS 128/ES 228 - Lecture 2 a 19

Classification issues 1. How many classes to use? 2. How to set class limits? CS 128/ES 228 - Lecture 2 a 20

How many classes to use? Dichotomous scale: n Each class quite heterogeneous n Placement of boundaries is extremely sensitive to data density & quality CS 128/ES 228 - Lecture 2 a 21

How many classes to use? Multi-class scale: n Classes more homogeneous n Large number of classes hard to interpret Note: density of symbols should match the quantitative order of the classes CS 128/ES 228 - Lecture 2 a 22

How to set class limits? 1. Constant intervals CS 128/ES 228 - Lecture 2 a 23

How to set class limits? 2. Equal class frequency CS 128/ES 228 - Lecture 2 a 24

How to set class limits? 3. Natural breaks in distribution CS 128/ES 228 - Lecture 2 a 25

3. Simplification Begins with choice of scale and number of classes Other issues: n Reduced dimensionality of line or area features n Smoothing lines and boundaries n Aggregation CS 128/ES 228 - Lecture 2 a 26

Reduced dimensionality CS 128/ES 228 - Lecture 2 a 27

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 2 a 28

Aggregation n Like smoothing, but refers to scale of spacing of objects CS 128/ES 228 - Lecture 2 a 29

4. Exaggeration Why, given scale limitations, would map makers make features or labels larger? n n Make symbols visible Separate features and symbols CS 128/ES 228 - Lecture 2 a 30

5. Symbolization Issues: n Realistic vs. abstract symbols n Size, texture, and density n Use of color CS 128/ES 228 - Lecture 2 a 31