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

CS 128/ES Lecture 2a2 Early mental maps are egocentric

CS 128/ES Lecture 2a3 Where would you like to live?

CS 128/ES Lecture 2a4 The geocentric map concept Based on: four cardinal directions 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 Lecture 2a5 What is a map? “Art is a lie which makes us realize the truth.” P. Picasso “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

CS 128/ES Lecture 2a6 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)

CS 128/ES Lecture 2a7 How does a map differ from reality? Size Dimensionality Amount of detail Symbolic presentation Static vs. dynamic ???

CS 128/ES Lecture 2a8 What about aerial photographs? Aren’t they realistic?

CS 128/ES Lecture 2a9 Cartography: the art & science of creating maps

CS 128/ES Lecture 2a10 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 Lecture 2a11 1. Selection Depends on: Purpose Data availability Size and scale of map

CS 128/ES Lecture 2a12 Selection: scale One of the most important choices – determines what can or cannot be included in the map

CS 128/ES Lecture 2a13 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 Lecture 2a14 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 Lecture 2a15 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 Lecture 2a16 Inset maps User must deal with multiple scales Rule: the inset always ends just short of the point of interest

CS 128/ES Lecture 2a17 Selection: coverage State maps minimize details in adjacent states Topographic maps omit detail in urban areas

CS 128/ES Lecture 2a18 Selection: time frame Maps are essentially snapshots Two rules: 1. Every map should be dated!! 2. Don’t trust the dates

CS 128/ES Lecture 2a19 2. Simplification Begins with choice of scale Other issues: Reduced dimensionality of line or area features Smoothing lines and boundaries Aggregation

CS 128/ES Lecture 2a20 Reduced dimensionality

CS 128/ES Lecture 2a21 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 Lecture 2a22 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 Lecture 2a23 3. Exaggeration Why, given scale limitations, would map makers make features or labels larger? Make symbols visible Separate features and symbols

CS 128/ES Lecture 2a24 4. Symbolization 1. Size, texture, and density

CS 128/ES Lecture 2a25 Issues of Symbolization 1. Size, texture, and density

CS 128/ES Lecture 2a26 Issues of Symbolization 1. Size, texture, and density

CS 128/ES Lecture 2a27 Issues of Symbolization 2. Use of color

CS 128/ES Lecture 2a28 Issues of Symbolization 3. Realistic vs. abstract

CS 128/ES Lecture 2a29 Symbolization Find here decisions about: Size, texture, and density Use of color Realistic vs. abstract symbols