Map Symbolization

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Lab 6: Symbology https://www.mapbox.com/osm-data-report/ Objective Learn cartographic considerations and strategies for representing map features Overview ❏ Generalization strategies ❏ Data Types ❏ Levels of Measurements ❏ Visual Variables Maps are created to serve a purpose. Images: http://www.sbmtd.gov/maps-and-schedules/system-map.html http://www.carolmendelmaps.com/mapsb/sb3.html http://lhcalligraphy.com/maps-santa-barbara-ca Maps are created to serve a purpose. When creating a map, it is necessary to generalize about the world in order to convey specific information. ❏ Cartographic generalization strategies: - Selection - Simplification - Combination - Locational shift - Exaggeration Cartographic generalization strategies: Selection Select & represent important features; omit unimportant ones. http://www.cartographicperspectives.org/index.php/journal/article/view/cp68-roth-et-al/html Cartographic generalization strategies: Simplification Simplify shapes of features to reduce complexity. http://www.cartographicperspectives.org/index.php/journal/article/view/cp68-roth-et-al/html Cartographic generalization strategies: Combination Combine features that are close together into a single feature. http://www.cartographicperspectives.org/index.php/journal/article/view/cp68-roth-et-al/html Cartographic generalization strategies: Locational Shift Adjust location of a feature to avoid overlap. http://www.cartographicperspectives.org/index.php/journal/article/view/cp68-roth-et-al/html Cartographic generalization strategies: Exaggeration Exaggerate characteristic aspects of a feature. http://www.cartographicperspectives.org/index.php/journal/article/view/cp68-roth-et-al/h tml ❏ Types of Map Data Qualitative – categorical, descriptive Quantitative – ordered, numerical ❏ Levels of measurement - Nominal Qualitative - Ordinal - Interval Quantitative - Ratio Different types of data require different symbolization strategies Nominal – categorically discrete, no orde • Qualitative data. E.g. State name or Class name • Cannot be arranged in some numeric order Ordinal – natural order • Qualitative data used for measuring rank • Can be arranged by some numeric order but there is no mathematical significance Temperature: ºF and ºC • Quantitative data. Used to measure data which does not have a true “zero” e.g. temperature http://www.wunderground.com/US/Region/US/Temperature.html http://newavessays.com/news/2009/02/p-38/ • Quantitative data. Used to measure data which has an absolute zero Data can be symbolized using ❏ Visual Variables Shape Hue Texture Size Graytone value Orientation Data can be symbolized using ❏ Visual Variables Shape Hue Texture Size Graytone value Orientation ❏ Visual Variables ❏ Visual Variables ❏ Visual Variables ❏ Visual Variables ❏ Visual Variables ❏ Visual Variables ❏ Visual Variables … Reminder! • All lab materials are on Gauchospace • Due date: Wednesday November 27th by 11:00 am Geog W12 Maps and Spatial Reasoning Lab 6: Map Symbolization OBJECTIVES Although seemingly objective representations of the real world, maps are subject to a high degree of subjectivity in content and presentation. In this exercise you will learn about the generalization inherent in cartography, as well as the different types of data, types of data, levels of measurement, and visual variables that are included on maps. We will examine the importance of using symbols appropriate to the data to understand how cartographic visualizations can be used reveal meaningful spatial trends or perhaps promote misleading interpretations. MATERIALS Internet Browser BACKGROUND Key Terms Generalization To employ strategic cartographic techniques that reduce the complexities of the real world for representation on a map. Techniques include selection, simplification, combination, locational shift, and exaggeration. Levels of measurement Categories of measurement according to how they can be treated mathematically. Measurements can be nominal, ordinal, interval, or ratio. Qualitative Involving distinctions based on qualities, kind, or type. Quantitative Involving the measurement of quantity or amount. Normalization To standardize or make consistent Introduction Maps are massive reductions of the reality they represent. If viewed in enough detail, the surface of the Earth can be infinitely complex. For the sake of clarity, much of reality is suppressed to make maps readable. Cartographers select relevant information and symbolization schemes to highlight what is important and exclude what is extraneous. As a result, geometric distortion, scaling, and graphic generalization of data are often unavoidable elements of cartographic representation. EXERCISE Part A. Generalization One means of generalization that cartographers employ is selection, the retention of more important features and the omission of the less important ones. Another technique is simplification, reducing complexity so that the major characteristics of a feature are still identifiable. Combination is a common form of generalization in which two or more similar features are grouped into one symbol or category. Cartographers may also use locational shifts which introduce a slight budge to a feature’s location to improve visibility of objects that may run together. In addition, features may be exaggerated for visibility or to indicate importance. Spring 2015 Page 1 of 9 Geog W12 Maps and Spatial Reasoning A portion of the London underground rail system is shown here to scale, with stations and lines in their geographic locations. Below is the same region on the official schematic map distributed by the London Underground. This map shows relative positions of stations along the rail lines. Transportation system maps typically emphasize topology, or connective relations, rather than geography. Spring 2015 Page 2 of 9 Geog W12 Maps and Spatial Reasoning 1. Examine the two maps of the London rail system. Explain in detail what generalization techniques were employed in creating the schematic diagram. What information was omitted to produce the schematic map? _____________________________________________________________________________________ _____________________________________________________________________________________ 2. Why is a schematic diagram preferred for transportation maps? _____________________________________________________________________________________ _____________________________________________________________________________________ A geographically accurate, interactive Tube Map can be found on the Tube Journey Planner (http://tubejp.com/). If you like, spend some time exploring the application to understand the complexities involved in mapping this extensive transit system. Part B. Representing Information Levels of Measurement Data can be qualitative, portraying a characteristic difference in kind or type, or quantitative, showing an amount difference in degree. All measurements can be subcategorized according to four levels. The nominal scale provides qualitative information such as name or class, in which ordering is meaningless. The ordinal scale, which assigns numbers to objects according to rank order, is quantitative but has no mathematical significance. For example, ranking states in order of preference indicates relative information, but performing mathematic operations on rank, such as taking a mean, make little sense. Interval is a category for numerical measurements that lack a true “zero” value or origin, such as the Celsius temperature scale or mean sea level. In contrast, ratio is a level of measurement at which numerical information is based on an absolute zero or origin, such as distance. Visual Variables The aim of cartography is to effectively communicate spatial information with a minimum of effort. In fact, much research has been dedicated to improving the comprehension of symbols, particularly on maps used by emergency responders. Various symbolization schemes are used to represent information on maps. Features on maps appear as one of three geometric symbol categories: points, lines, or areas. These symbols can differ in size (varying in length, width, or area), shape, gray tone value (from light to dark), texture (varying in pattern), orientation (changing in alignment) or hue (differing in color). There is a logic to the usage of these six visual variables. Each excels in portraying different qualitative or quantitative variations and levels of measurement. Typically, to display qualitative information, hue, shape, or texture variables are used. To display amount or counts, different sizes of symbols are used. To display intensity or density, gray tone is used. To display movement or direction, orientation is used. A mismatch in data and appropriate symbols may lead to misjudgments about the map message. As an example, hue and quantitative information usually is not a good pairing, but there are exceptions. For example, using the traffic light color scheme (green, yellow, red) to indicate rankings from best to worst, or using the blue to red gradient to represent temperature because people readily associate these colors to cold and hot. Spring 2015 Page 3 of 9 Geog W12 Maps and Spatial Reasoning The following chart depicts the six visual variables and the information they best communicate, according to convention on map semiotics developed by Jacque Bertin, a French cartographer. Visual Variable Point Line Area Best to show Size Quantitative  Amount  Counts Shape Qualitative  Name  Category Graytone value Quantitative  Intensity  Density  Ranking Hue Qualitative  Name  Category Texture Qualitative  Name  Category Orientation Quantitative  Movement  Direction Based on Monmonier, How to Lie with Maps. Spring 2015 Page 4 of 9 Geog W12 Maps and Spatial Reasoning Examples: Good use of Hue - Qualitative Political map with country names population? Poor use of Hue - Quantitative Population by country. Which has highest Graytone would be better for comparisons. Spring 2015 Page 5 of 9 Geog W12 Maps and Spatial Reasoning 3. For the following maps, list this visual variable combination in use (ex: hue and area, size and point, shape and point, etc), the levels of measurement represented (nominal, ordinal, interval, or ratio), and discuss if the symbolization is appropriate. There can be more than one visual variable combo, so list all that apply. (click on maps to enlarge) EXAMPLE EXAMPLE a. MLB United Countries of Baseball Fan Map * Visual variable combination(s): Area and hue * Level(s) of measurement: Nominal * Appropriate? Yes, hue is appropriate for nominal data because it is qualitative and does not have an intensity or ranking order. Source: http://www.unitedcountriesofbaseball.com. 2007. b. Life in Los Angeles with modified Chernoff faces. * Visual variable combination(s): * Level(s) of measurement: * Appropriate? Source: Eugene Turner. 1977. http://mapdesign.icaci.org/2014/12/mapcarte-353365-life-in-los-angeles-by-eugeneturner-1977/ Spring 2015 Page 6 of 9 Geog W12 Maps and Spatial Reasoning c. Napoleon’s March on Moscow. * Visual variable combination(s): * Level(s) of measurement: * Appropriate? Source: Charles Minard. 1861. d. Shape of America’s Population Cartogram. NY Times 2000. * Visual variable combination(s): * Level(s) of measurement: * Appropriate? Source: Andrew Phillips. The New York Times. Dec 2000. Spring 2015 Page 7 of 9 Geog W12 Maps and Spatial Reasoning Part C. Classification Thematic maps show the spatial distribution of one or more specific themes for geographic areas. This portion of the lab will focus on choropleth maps, a commonly used thematic map in which color or shading of area features are used to represent categories of attribute values. These maps can indicate spatial patterns of statistical data and are usually mapped onto political boundaries, such as state or county. Assuming there are no problems with the original data, some sources of problems with choropleth maps are the size of areal unit selected (state, county, census tract, etc). The spatial unit makes a difference in the story a map tells. A pattern that is evident in at a neighborhood scale may be washed out when generalized to a state level or vice versa. Presidential Election 2008 results by State and by County Selection of number of data classes, how they are divided, and the color scheme also tell a story. Different sets of class breaks applied to the same data can yield different looking choropleth maps, as in the figure to the right. Data can be classed using equal intervals, in which each has the same width as others (ex: 1-20, 21-40, 41-60). Commonly, this can result in large differences between the number of cases in each class, and some classes may not have any cases. With equal frequency classification (quantiles), each class has the same, or close to the same, number of cases. This is equivalent to the idea of percentiles in statistics. Natural breaks classification is based on the idea that data sometimes fall into clear groups. Although this can be done “by eye,” usually statistical methods are used to form natural groups that minimize variance, means, medians, and outliers. Alternatively, choropleth maps can be classless or unclassed. Areas are shaded based on individual values, not divided into classes, on a continuous scale. Although this makes it harder to mislead a map user, it results in more complex display patterns that are difficult to interpret and remember. A cartographer can also select arbitrary class breaks to emphasize certain data or introduce bias, a tactic of which map readers should be critical. Spring 2015 Page 8 of 9 Geog W12 Maps and Spatial Reasoning 4. Take a look at the map below of United Stated Obesity published by Calorie Lab in 2008. Source: http://calorielab.com/news/2008/07/02/fattest-states-2008. Last accessed Sept 2009. Discuss how map symbolization is used to convey a particular message. What are the colors used to signify? Would you consider this map to be objective? Be sure to evaluate the classification scheme, selection of class boundaries, and areal units. _____________________________________________________________________________________ _____________________________________________________________________________________ Part D. On your own 5. Find a recent map online, in a magazine, or newspaper and analyze its symbolization. Discuss the visual variables, any possible issues you may have with its representation of data, and it’s classification scheme. Attach a copy of your map to the back of the lab. _____________________________________________________________________________________ _____________________________________________________________________________________ RELATED LINKS ColorBrewer by Cindy Brewer, Penn State University.  The Original Color Brewer (http://www.personal.psu.edu/cab38/ColorBrewer/ColorBrewer_intro.html)  Color Brewer 2 (http://colorbrewer2.org/) Spring 2015 Page 9 of 9 Geog W12 Maps and Spatial Reasoning Lab 6: Symbology Name: Section: Part A. Generalization 1. Examine the two maps of the London rail system. Explain in detail what generalization techniques were employed in creating the schematic diagram. What information was omitted to produce the schematic map? (1) 2. Why is a schematic diagram preferred for transportation maps? (1) Part B. Representing Information 3. For the following maps, list this visual variable combination in use (ex: hue and area, size and point, shape and point, etc), the levels of measurement represented (nominal, ordinal, interval, or ratio), and discuss if the symbolization is appropriate. There can be more than one visual variable combo, so list all that apply. (You can download these maps from GauchoSpace and use any image viewer to view enlargements.) (9) EXAMPLE EXAMPLE a. MLB United Countries of Baseball Fan Map * Visual variable combination(s): Area and hue * Level(s) of measurement: Nominal * Appropriate? Yes, hue is appropriate for nominal data because it is qualitative and does not have an intensity or ranking order. Source: http://www.unitedcountriesofbaseball.com. 2007. Spring 2015 Page 1 of 4 Geog W12 Maps and Spatial Reasoning b. Life in Los Angeles with modified Chernoff faces. * Visual variable combination(s): * Level(s) of measurement: * Appropriate? Source: Eugene Turner. 1977. http://mapdesign.icaci.org/2014/12/mapcarte-353365-life-in-los-angeles-by-eugeneturner-1977/ c. Napoleon’s March on Moscow. * Visual variable combination(s): * Level(s) of measurement: * Appropriate? Source: Charles Minard. 1861. Spring 2015 Page 2 of 4 Geog W12 Maps and Spatial Reasoning d. Shape of America’s Population Cartogram. NY Times 2000. * Visual variable combination(s): * Level(s) of measurement: * Appropriate? Source: Andrew Phillips. The New York Times. Dec 2000. Part C. Classification 4. Take a look at the map below of United Stated Obesity published by Calorie Lab in 2008. Source: http://calorielab.com/news/2008/07/02/fattest-states-2008. Last accessed Sept 2009. Discuss how map symbolization is used to convey a particular message. What are the colors used to signify? Would you consider this map to be objective? Be sure to evaluate the classification scheme, selection of class boundaries, and areal units. (3) Spring 2015 Page 3 of 4 Geog W12 Maps and Spatial Reasoning Part D. On your own 5. Find a recent map online, in a magazine, or newspaper and analyze its symbolization. Discuss the visual variables, any possible issues you may have with its representation of data, and it’s classification scheme. Paste a copy of your map here. (5) Spring 2015 Page 4 of 4
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