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1 Everything on a ma is a symbol. A ma symbol is a visual mark systematically linked to the data and concets shown on a ma. Consciously and critically Symbolization choose 9Ma symbols that hel your ma do what you want it to do. symbol by relationshi Some ma symbols intuitively suggest general kinds of data. A ma showing the oulation of different cities uses circle sizes from small to large: sizes vary in amount, as do the data. symbol by resemblance A ma showing restaurants, antique stores, and museums in a town uses different shaes: shaes vary in kind, as do the data. n n symbol by convention Other ma symbols look like articular data or concets. A ma showing the location of airorts uses an airlane symbol for airorts: the symbol looks like an airlane, and is associated with an airort. Mas in a war atlas use red symbols to show the location of battles: the symbol looks like an exlosion, and is associated with a battle. Peole often associate red with danger or conflict. Some symbols make sense even though they may not entirely make sense. The U.S. Geological Survey uses the Christian cross to symbolize all laces of worshi - church, mosque, synagogue. We know what they mean, though it s not very olitically correct. A ma showing the earth s oceans uses blue for water. But is water out in the real world blue? Not usually. Blue on a ma, however, suggests water - it s a convention. If you deart from conventions (color your oceans their actual color) you could confuse your ma s readers. 196

2 n Basic ma symbolization issues include: 1Different kinds of data: data at oints, along lines, and in areas; differences in kind and number; individual or aggregate data. Homes with Radon location Homes with Radon er county 2The visual variables: choosing ma symbols. The visual variable size readily imlies......variation in quantity. The visual variable shae readily imlies......variation in quality. 3Symbolizing aggregate data: guidelines for choosing among choroleth, graduated symbol, dot, and surface mas. 197

3 Visual variables described and illustrated 2b Understanding the nature of visual variables will hel you select ma symbols which clearly make the oint you want your ma to make. shae Ma symbols with different shaes intuitively imly differences in quality. A square is not more or less than a circle, but is different in kind. Ma symbol shaes can be ictorial or abstract. Poor use of shae: Active Hate Grous, Shae is a oor choice for showing quantitative data Alaska Hawaii ü using shae makes it difficult to see the atterns on the ma, as the symbols do not suggest the order (low to high) in the data. Good use of shae: Shae is a good choice for showing qualitative data Dominant Hate Grou, 2003 ü different shaes suggest the qualitatively different grous. 202 KKK Neo-Nazi Black Searatist Neo-Confederate Christian Identity Racist Skinhead Alaska Hawaii

4 3a aa Symbolizing aggregate data: choroleth mas The choroleth ma is one of the most common maing techniques for data groued into areas - counties, rovinces, states, countries, etc. Choroleth mas vary the shading of each area along with the data value associated with the area. aroriate data ü derived data (densities, rates), sometimes totals Maing total numbers with a choroleth ma is often not recommended, articularly when the areas on the ma vary in size. A large area may have more eole simly because it covers a larger area. If you ma totals (bold, below) and classify the data, an area with 100 eole will likely be in a different class than the area with 500 eole. The visual difference between the areas is the result of the unequal size of the areas. Maing derived data, like oulation er square mile, takes into account the varying size of areas on the ma. If you ma densities (bold, below) and classify the data, both areas have 10 eole er square mile and will be in the same class. 100 eole 10 sq. miles 500 eole 50 sq. miles 100 eole 10 sq. miles 500 eole 50 sq. miles Maing totals with a choroleth ma can be OK! A marketing comany mas the total number of Polish-seaking U.S. citizens by county in the U.S., to assist in a lan to market Polish greeting cards. In this case, what is most imortant is where the most Polish-seaking folks are. But do consider a graduated symbol ma for totals: it may better serve your needs. Your goals for your ma drive ma choices! There is no absolute best kind of data for a choroleth ma indeendent of your goals for your ma. Be aware of the roblem of maing totals with a choroleth ma, but if your goals require totals, just do it. Then create a graduated symbol ma of the same data, and comare the mas. Please use your brain when making mas. 212

5 design issues shading Poor value & legend: ü dark means less is not intuitive. ü smaller values at to of legend are not intuitive. Poor value & boundaries: Good value & legend & boundaries: Farms er sq. mile ü dark means more to most eole. ü non-continuous legend, with larger values at the to and a title which exlains the numbers in the legend. ü overall smoother feel without black and white in addition to removing the roblems they cause. ü boundaries less dominant but distinct. ü black blends with boundaries. ü white suggests no data. ü boundaries stand out too much. 213