SIMS 247 Lecture 3 Graphing Basics Continued January

SIMS 247 Lecture 3 Graphing Basics, Continued January 27, 1998 Marti Hearst SIMS 247

Today • • • Finish graphing basics Demonstrate on web access example Discuss Tufte’s Data Ink Maximization principle Marti Hearst SIMS 247

Types of Symbolic Displays (Kosslyn 89) • Graphs • Charts • Maps • Diagrams Marti Hearst SIMS 247

Types of Symbolic Displays • Graphs – at least two scales required – values associated by a symmetric “paired with” relation • Examples: scatter-plot, bar-chart, layer-graph • Charts – discrete relations among discrete entities – structure relates entities to one another – lines and relative position serve as links • Examples: family-tree, flow-chart, network diagram Marti Hearst SIMS 247

Types of Symbolic Displays (cont. ) • Maps – internal relations determined (in part) by the spatial relations of what is pictured – labels paired with locations • Examples: map of census data, topographic maps • Diagrams – schematic pictures of objects or entities – parts are symbolic (unlike photographs) • Examples: how-to illustrations, figures in a manual Marti Hearst SIMS 247

Standard Graph Types • • Scatter plots Line graphs Time series (strip charts) Dot plots Bar Charts Pie Charts Layer Graphs Marti Hearst SIMS 247

Choosing the Axes • Independent vs. Dependent variables – the dependent variable changes relative to the independent one • sales against season • tax revenue against city D I • What happens when there is more than one independent variable? – Most important is assigned to X axis – Other(s) differentiated by mark symbol Marti Hearst SIMS 247

Basic Types of Data • Qualitative -- nominal – no inherent order (for comparisons) • city names, types of diseases, . . . • Qualitative -- ordinal – ordered, but not at measurable intervals • first, second, third, … • cold, warm, hot • Quantitative -- interval and ratio Marti Hearst SIMS 247

Combining Data Types in Graphs (adapted from Kosslyn 89) Nominal by Nominal: Use a Chart Marti Hearst SIMS 247

Scatter Plots • Qualitatively determine if variables – highly correlated • linear mapping between horizonal & vertical axes – nonlinear relationship • a curvature in the pattern of plotted points – low correlation • spherical, rectangular, or irregular distributions • Place points of interest in context • apply shapes or color to points representing special entities, see where they end up Marti Hearst SIMS 247

Time Series • • • Change over time Facilitates finding trends Also known as “strip charts” Marti Hearst SIMS 247

Web Page Visit Behavior • • • What are our goals? What questions do we want to answer? What kind of data might we collect? How might we convey this information? Who is the audience? Marti Hearst SIMS 247

Web Access Data Types (consider the possible combinations) Marti Hearst SIMS 247

length of access very long medium short 45 40 35 30 25 20 15 10 5 0 # of accesses URL length of access length of page # of accesses Hypothetical Graphs length of access url 1 url 2 url 3 url 4 url 5 url 6 url 7 days # of accesses length of page Marti Hearst SIMS 247

How to Show Link Traversal? How to link together the to-links and from-links in our web access example? Marti Hearst SIMS 247

Charts • Structural / organizational material – nominal by nominal • Specify relationships among discrete members of a set • Not relating on quantitative dimensions • Components of Charts (Kosslyn 89): – directed vs. undirected links – how many types of links – types of mapping e. g. , one-to-one, one-to-many, many-to-many • Tables can also be considered charts Marti Hearst SIMS 247

Mapping Types in Charts one-to-one one-to-many-to-many Marti Hearst SIMS 247

Chart Example (organizational chart) Marti Hearst SIMS 247

Chart Example (Software architecture, labels omitted, by Chen and Hong 97) Marti Hearst SIMS 247

How to show link patterns in web access example? Problem: only shows one step Think about this for next time. Marti Hearst SIMS 247

Graph/Chart Hybrids • • • An area for innovation Combine Structure with Graphics Example: Docuverse (Spring et. al 96) • structure: file system structure • graphics: color -> file age • Example: Tile. Bars (Hearst 95) • structure: document subtopics (columns) • structure: faceted query (rows) • graphics: gray-level -> number of hits Marti Hearst SIMS 247

Marti Hearst SIMS 247 Docuverse (Spring et. al 96)

Tile. Bars (Hearst 95) Marti Hearst SIMS 247

Discussion: Tufte’s Notion of Data Ink Maximization • What is the main idea? – draw viewers attention to the substance of the graphic – the role of redundancy – principles of editing and redesign • What’s wrong with this? What is he really getting at? Marti Hearst SIMS 247

Next Time: Multidimensional Graphing How do we handle cases with more than three variables? – Multiple views – Scatterplot matrix – Parallel Coordinates – Tufte examples: combine space and time – Interaction/animation across time Marti Hearst SIMS 247

References for this Lecture • Kosslyn, Stephen M. Understanding Charts and Graphs. Applied Cognitive Psychology, 3, 185 -226. 1989 • Spring, Michael B. , Morse, Emile, and Heo, Misook. Multi-level Navigation of a Document Space. http: //www. lis. pitt. edu/~spring/mlnds/nlnds/mlnds. html • Schall, Matthew. SPSS DIAMOND: a visual exploratory data analysis tool. Perspective, 18 (2), 1995. http: //www. spss. com/cool/papers/diamondw. html • Hearst, M. Tile. Bars, Visualization of Term Distirubtion in Full Text Information Access. Proceedings of ACM SIGCHI 95. • Tufte 83 Marti Hearst SIMS 247