GIS Presentation Issues in Mapping Data

1. GIS PresentationIssues in Mapping Data Jennifer Ailshire and Jeff Strickland Population Studies Center University of Michigan Portions of this PPT were adapted from an original version created by Stephen Matthews, Population Research Institute, Pennsylvania State University

2. Elements of Geographic Information • GIS is layer-based.  GIS datasets represent collections of individual features with their geographic locations and shapes as well as with descriptive information stored as attributes.   There are four fundamental types of geographic representations: • Attributes • Features (collections or points, lines, and polygons) • Imagery • Continuous surfaces (such as elevation) • We will work primarily with Attributes and Features. • source: Support.ESRI.com

3. Attributes Descriptive attributes are managed in tables, which are based on a series of simple, essential relational database concepts. A relational database provides a simple, universal data model for storing and working with attribute information. Key relational concepts include: • Descriptive data is organized into tables. • Tables contain rows. • All rows in a table have the same columns. • Each column has a type, such as integer, decimal number, character, date, and so on. • A series of relational functions and operators (SQL) is available to operate on the tables and their data elements. source: Support.ESRI.com Source: Support.ESRI.com

4. Features - Points, lines, and polygons Points define discrete locations of geographic features too small to be depicted as lines or areas, such as well locations, telephone poles, and stream gauges. Points can also represent locations such as address locations, GPS coordinates, or mountain peaks. Lines represent the shape and location of geographic objects too narrow to depict as areas (such as street centerlines and streams). Lines are also used to represent features that have length but no area such as contour lines and administrative boundaries. (Contours are interesting, as you'll read later on, because they provide one of a number of alternatives for representing continuous surfaces.) Polygons are enclosed areas (many-sided figures) that represent the shape and location of homogeneous features such as states, counties, parcels, soil types, and land use zones. In the example below, the polygons represent Parcels. source:support.esri.com

5. Edward Tufte The Visual Display of Quantitative Information ends with the following paragraph: "What is to be sought in designs for the display of information is the clear portrayal of complexity. Not the complication of the simple; rather the task of the designer is to give visual access to the subtle and the difficult - that is, the revelation of the complex." (Edward Tufte, 1983 p. 191)

6. Know your data, your message, etc. Many cartographic and statistical graphics books begin by considering the measurement level associated with the data (i.e., nominal [qualitative], ordinal [ranked], interval or ratio [quantitative]).   Knowing the measurement level characteristics the data should determine the type of thematic map (or graph) to design.

7. Classes of Geographical Data Measurement Levels Categories of Map Symbols Visual Dimensions of Symbols Points Lines Areas Surfaces Nominal Ordinal Interval Ratio Points Lines Areas Size Shape Pattern Orientation Arrangement Texture Color Hue Value tone Intensity

8. Geographical phenomena and their conventional symbolization (adapted from Dent, 1985, Table 4.4) Working with POINT data Symbolization Most appropriate Map Option Design/Form Nominal point symbol = Graduated symbol map (one size) Ordinal point symbol = Graduated symbol map (2 or more sizes or one size different shape/color, etc.) Interval/ ratio point symbol = Dot density maps

9. Geographical phenomena and their conventional symbolization (adapted from Dent, 1985, Table 4.4) Working with LINE data Symbolization Most appropriate Map Option Design/Form Nominal line symbol = Graduated symbol map (to produce lines of one size) Ordinal line symbol = Graduated symbol map (to produce line map of 2 or more line widths or one line width with different line style or color)

10. Geographical phenomena and their conventional symbolization (adapted from Dent, 1985, Table 4.4) Working with LINE data Symbolization Most appropriate Map Option Design/Form Interval/ ratio line symbol = Range or graduated symbol map (to produce line maps where the line width varies in proportion to line attribute data values

11. Geographical phenomena and their conventional symbolization (adapted from Dent, 1985, Table 4.4) Working with AREA data Symbolization Most appropriate Map Option Design/Form Nominal area symbol = Individual theme or range map (one category) Ordinal area symbol = Individual theme or range map (2 or more categories) Interval/ ratio area symbol = Range map

12. Map Elements In order to present data in a meaningful way we must vary the of the symbols, and we must do so systematically by adjusting their graphic quality. Marks on a map can be made to appear more or less distinctive. The fact that symbols on a map are large enough to be seen does not in itself provide clarity and legibility. An extra graphic component is necessary …visual contrast.

13. Color Color is a cartographic minefield. While color can be used to make a map visually attractive the complexity and seductiveness of color can easily overwhelm the map reader. Indeed,naïve use of color and ignorance about how best to use color in mapping can devalue the map and its intended message.

14. Color Color used effectively can help simplify and clarify map design. Similarly, a smart choice of colors can also facilitate printing and reproduction of maps (even with limited resources) using only a few colors or even just black and white shading (greytone) or patterns. Color should only be used to add meaning to, and better understanding of, a map. Too many choices of color or unwise choices too often distract rather than improve map interpretation.

15. Color Connotations Color can prompt certain aesthetic reactions and that this can have implications for map design and effective communication.

16. Color Combinations Color can be useful in developing the figure and ground organization on the map and by allowing for greater map design options. Generally warm colors take on figure qualities better than cool which tend to make good grounds.  

17. Color Combinations It should be noted that this is a partial list and also any modification of saturation and lightness will affect the figure-ground contrast.

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26. Titles and Legends Specific to maps but also relevant for graph design, the title and legend inform the reader, what is being mapped/graphed (title) and how that is being accomplished (legend). That is, the title and legend have two different complementary functions. However, frequently, map designers confuse the individual objectives of these two pieces of text and duplicate some words in both.

27. Titles and LegendsThe title should reflect the map theme and the symbolization used and it must be complemented by the legend. The legend heading should identify the mapped data and provide guidance on how to interpret the map symbols. If the variable name is in the title, the legend typically provides clarification on the measurement or metric used (e.g., percent, ratio, kilograms, etc.). Listing the variable name in both the title and legend is redundant. Similarly, words such as "map", "legend", "scale" are all redundant on any well designed map.

28. Overall Layout A common mistake in map design is to underestimate the significance of the the component parts the titles, text, images/maps/graphs, and legend. positioning

29. Overall Layout – Maps A successful map begins with layout design. Layout design considers the effective use of space within the map frame. In essence, the sizing and proportioning the map must be followed by an economical arrangement of map and other elements within the frame. Other elements can include, title, legend, scale bar, footnotes and other text (e.g., source material and date of construction), additional graphics (including map insets), photographs, etc.

30. Overall Layout Some maps do not make effective use of the available space and can appear to be unbalanced. 

31. Overall Layout Some page layouts may be more efficient . 

32. General Guidelines for Overall Layout Avoid top-heavy or unbalanced arrangements; Treat the map/graph area as an element that can be positioned to make the best use of space and rearrange map/graph elements to achieve greater internal order; Do not shrink the map/graph area to create free space at the edges. Instead, position the map/graph so that title, legend and other elements can be placed; And remember the graphic variables and especially those that facilitate easy visual contrasts between map/graph elements.

33. General Guidelines for Mapping Layout - 1 Areas of highest value or greatest densities should be assigned the darkest colors (ideally texture and pattern should be held constant). Increasing the number of categories increases the complexity of the mapped/graph pattern. Map complexity due to data classification issues may be compounded when there are a large number of regions to be mapped, when there are substantial differences in the size of map regions and when there is little spatial regularity (shape);

34. General Guidelines for Mapping Layout - 2 Grey-tones cannot be separated easily and therefore the map cannot be easily read. It is recommended that no more than six data classifications are used in grey-tone maps. If more than six data classifications are necessary the map should be re-evaluated and perhaps be re-mapped as two separate maps. A map should only try to emphasize one or two patterns. More than this and the map begins to become confusing. Indeed, the focus of the map (the pattern(s)) should be clear;

35. General Guidelines for Mapping Layout - 3 All labels should be used precisely; Colors (and patterns) should be well chosen to reflect whether or not a map is communicating data (qualitative or quantitative) effectively; Symbols should be easily distinguishable and make intuitive sense (when using bar and pie-charts or complex graduated symbols make sure that the graphic symbols can be read).

36. The End