Map Interpretation CS 128ES 228 Lecture 3 b

Map Interpretation CS 128/ES 228 - Lecture 3 b 1

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

Magnetic North Pole n n n 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 CS 128/ES 228 - Lecture 3 b 3

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

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

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

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

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

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

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

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

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

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

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