CS 128/ES 228 - Lecture 3b 1

Map Interpretation

CS 128/ES 228 - Lecture 3b 2

What is North? There are three

“kinds” of north

Magnetic North Grid North True North

CS 128/ES 228 - Lecture 3b 3

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

CS 128/ES 228 - Lecture 3b 4

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”

CS 128/ES 228 - Lecture 3b 5

So what’s the difference?

CS 128/ES 228 - Lecture 3b 6

A Spectrum Revisited

How “honest” is the data?

As true as Not everything Deliberatethe world matches lies

Image Maps Line Maps Cartograms

Cartographer Influence Increasing

CS 128/ES 228 - Lecture 3b 7

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

CS 128/ES 228 - Lecture 3b 8

What are the “dimensions”? Color

Quantity

Shape

Fill Pattern

CS 128/ES 228 - Lecture 3b 9

Multivariate Symbols Multivariate symbols

Are very compact, but… Dimensions can be hard to interpret,

and… Can cause information overload

Lesson: Use them with care

CS 128/ES 228 - Lecture 3b 10

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

CS 128/ES 228 - Lecture 3b 11

Spotting the “lies”

On the topos provided, find examples of each of the following “lies” Aggregation Exaggeration Selection Deception?

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When is appropriate to “lie” with a map? Aggregation

Exaggeration

To convey a message

For amusement?

CS 128/ES 228 - Lecture 3b 13

Who went out of their way?

Choice of projection has a great influence on perception of distance!

CS 128/ES 228 - Lecture 3b 14

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