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 (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 5 steps of cartography: 1.Selection 2.Classification 3.Simplification 4.Exaggeration 5.Symbolization See textbook, Box 2.3 (p. 26) for a different list

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

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 1:24,000 Coverage 7 ½ minute topographic quadrangle  Scale line

CS 128/ES Lecture 2a14 Large and small scales Large scale: a given feature looks large Small scale: 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: - inset maps - locator 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. Classification Continuous vs. discrete features There are many ways to represent continuous features on a map Beware of the boundaries – they’re not real

CS 128/ES Lecture 2a20 Classification issues 1.How many classes to use? 2.How to set class limits?

CS 128/ES Lecture 2a21 How many classes to use? Dichotomous scale: Each class quite heterogeneous Placement of boundaries is extremely sensitive to data density & quality

CS 128/ES Lecture 2a22 How many classes to use? Multi-class scale: Classes more homogeneous Large number of classes hard to interpret Note: density of symbols should match the quantitative order of the classes

CS 128/ES Lecture 2a23 How to set class limits? 1. Constant intervals

CS 128/ES Lecture 2a24 How to set class limits? 2. Equal class frequency

CS 128/ES Lecture 2a25 How to set class limits? 3. Natural breaks in distribution

CS 128/ES Lecture 2a26 3. Simplification Begins with choice of scale and number of classes Other issues: Reduced dimensionality of line or area features Smoothing lines and boundaries Aggregation

CS 128/ES Lecture 2a27 Reduced dimensionality

CS 128/ES Lecture 2a28 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 2a29 Aggregation Like smoothing, but refers to scale of spacing of objects

CS 128/ES Lecture 2a30 4. Exaggeration Why, given scale limitations, would map makers make features or labels larger? Make symbols visible Separate features and symbols

CS 128/ES Lecture 2a31 5. Symbolization Issues: Realistic vs. abstract symbols Size, texture, and density Use of color