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UW-Madison GEOG 370 - Scale and Generalization

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Scale and generalizationGEOG 370 1st Edition Lecture 4 Outline of Last Lecture I. Map projection mechanicsa. Aspectb. CenteringII. Map projection distortions Outline of Current Lecture II. The Power of MapsIII. ScaleIV. Generalization Current LectureScale and generalization -The power of maps • Maps abstract reality, they are not reality itself - Map: an authored representation of geographic phenomena - Representation: A thing that stands for another thing- Abstract representation: a thing that stands for another thing and that retains only the information content of the original thing that is relevant to the purpose of the representation• Maps are powerful because they abstract the reality they represent • Never attempt to retain everything • Example: -1924 state of California commissioned a 3D terrain model of entire state. About sizeof football field and height of person ($20 million) Realized it didn't help very much and got lost These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.-A map that doesn't abstract is the same as wandering around on the earth and looking for yourself • The cartographic problematic:-Place --> human imagination --> place • We are constantly changing and wanting change which keeps geography going -In order to create a abstraction of reality that makes complex geographic phenomena information useful and useable, uncertainty is introduced into the representation (and into the knowledge constructed from the representation) as a necessary compromise• Power comes from the abstraction, but at the price of uncertainty-Geography (abstraction -->) representation• ---------------> power <-------------uncertainty• The challenge is finding the optimal degree of abstraction for your map purpose -Which is why cartographers should be geographers first or they won't understand nature of the geography behind it • Example: American/English dialects map shows that he wanted you to see all of it, which leads you unable to read any of it. Series of maps would've even helped.Great data set, but not great communication tool. • Scale-Scale first - Geographic scale: the size/extent at which geographic phenomena exist -Geographic patterns and process vary by geographic scale• Example: looking at drivers of cervical cancer (scale generalization map) across U.S. From multi-scale analysis looking at key clusters of elevated numbers cervical cancer.- Cartographic scale: the ratio between distance measurements on the map and distance measurements on the earth (the relationship)• Maps are nor just models, they are scale models #ReferenceGlobe- Example of cervical cancer map and the small line at bottom of map to show that itequals 100 miles, scale- Indications of cartographic scale (3):• You can apprise the map user on the amount of abstraction through an indication of cartographic scale - Representation fraction ( RF ): the actual ratio of a measurement on the map to those on the earth• Always '1' to something, use a rounded number • Small scale: a map with a small RF, resulting in a large spatial extent (large geographic scale) - 1/250,000=0.000004• Large scale: large RF, resulting in a small spatial extent (small geogepahic scale) - 1/5,000=0.0002• Scale factor: the cartographic scale at a given location on the map compared to the cartographic scale at the standard line(s)/point(s)- Varies across map - SF=1 at standard lines/points, true scale - Example: • Class: cylindrical, Case: tangent, Touching at one standard line, compute by ratio/ratio. Growing scale factor, growing scale, conceptually zooming in, getting larger • Secant, smaller between standard lines• Planar larger when moving away • Pro: unit-less, concise • Con: cannot resize or post digitally, conceptually difficult to understand, as no benchmark example is given.• Verbal description: a verbal description of the cartographic scale comparing two distances - Pro: conceptually easier for a user to understand, compared to RF- Con: cannot resize or post digitally, often need to convert united to measure distances • "One inch is equal to one mile"• Example: map scales 1 inches = ... - Your screen changes • Graphic bar/ Scale bar: a graphic depiction of the cartographic scale using a line to show a benchmark example distance- Use thumb, use rounded, meaningful unite for subdivisions - Pro: can resize or post digitally, easier to measure with a ruler- Con: takes up more map space, poor on small scale maps, as it encourages measurement• Considering pairing two - Generalization as a process- Generalization: the basics • Abstraction is more than changing scale - Not just a photo reduction • Example: United airlines flight map of domestic airline routes- Problem: photo reduction - Not just showing data• Example: map of all streets in America. - Not useful at all • "The act of generalization gives the map it's reason to


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