1. CS 128/ES 228 - Lecture 3b1 Map Interpretation

2. CS 128/ES 228 - Lecture 3b2 What is North? There are three “kinds” of north Magnetic North Grid North True North

3. CS 128/ES 228 - Lecture 3b3 Magnetic North Pole Lines that point to “magnetic north” point to the magnetic north pole on earth. This location “moves” Currently about 1000 miles off at 81.3°N,110.8°W

4. CS 128/ES 228 - Lecture 3b4 Geographic North Pole Always found at same place (90° North Latitude) Famous as home of Santa Claus. Lines on a map that point to the geographic North pole represent “True North” Lines on a map parallel to the central meridian represent “Grid North”

5. CS 128/ES 228 - Lecture 3b5 So what’s the difference?

6. CS 128/ES 228 - Lecture 3b6 A Spectrum Revisited How “honest” is the data? As true as Not everything Deliberate the world matcheslies Image Maps Line MapsCartograms Cartographer Influence Increasing

7. CS 128/ES 228 - Lecture 3b7 One Cartographic Choice Use of symbols A single use for each symbol is clearest, but… Every symbol takes up space on the map… Thus, we sometimes use multi-dimensional symbols

8. CS 128/ES 228 - Lecture 3b8 What are the “dimensions”? Color Quantity Shape Fill Pattern

9. CS 128/ES 228 - Lecture 3b9 Multivariate Symbols Multivariate symbols Are very compact, but… Dimensions can be hard to interpret, and… Can cause information overload Lesson: Use them with care

10. CS 128/ES 228 - Lecture 3b10 A cartographic concern The interaction between choice of symbol and choice of scale is VERY important It is often ignored ArcMap permits you to display symbols (okay, layers with symbols) only at certain scales

11. CS 128/ES 228 - Lecture 3b11 Spotting the “lies” On the topos provided, find examples of each of the following “lies” Aggregation Exaggeration Selection Deception?

12. CS 128/ES 228 - Lecture 3b12 When is appropriate to “lie” with a map? Aggregation Exaggeration To convey a message For amusement?

13. CS 128/ES 228 - Lecture 3b13 Who went out of their way? Choice of projection has a great influence on perception of distance!

14. CS 128/ES 228 - Lecture 3b14 Conclusions Designing a map is like writing an essay – you can only do a decent job if you know What you wish to convey, and Who your audience is… The ultimate arbiter is the user