Effective Graphing for Cartographers SP 240 Cartography Alex Chaucer

Spatial Information Technology Center What is a graph? Must have a mathematical basis for construction Chart and diagram can be used for those such as drawings, pictograms, and organization-based drawings for which there may be no mathematical basis Philosophical Foundations 1.Graphicacy – skill necessary for communication of relationships that cannot be expressed with words or mathematics (other forms – literacy, numeracy, articulacy) 2.Graphic Communication is a part of human communication. Human communication is composed of 1. Communicator (the one “sending”) 2. Interpreter (the reader) 3. Communication content (the message) 4. Communication situation (perceived need to communicate)

Spatial Information Technology Center Brief History of Graphing Pre-Christian Times early gridding attempts at Lat/Long geometry Middle Ages planetary graphs Age of Enlightenment censuses, analytic geometry, early statistical graphs Age of Enthusiasm several European statistical conferences Early 19 th Century early textbooks on graphics, attempts at standards Modern Day graphing aided by microcomputers

Spatial Information Technology Center Perception and the Graph Tasks from simple  more complex Most Accurate to least accurate (more perceptual problems) 1. Position along a common scale 2. Position along identical, nonaligned scales 3. Length 4. Angle-slope 5. Area 6. Volume 7. Color hue-color saturation-density

Spatial Information Technology Center Elements of the Standard Graph Data region Scale lines Vertical Scale Horizontal Scale Scale labels Data path Reference line Markers Key, legend Data labels Titles Data sources

Spatial Information Technology Center Graph Planning in the Visual Hierarchy Similar concepts to design involved in creating a map Contrast can be used to get the reader’s attention Grid may be beneficial to include

Spatial Information Technology Center The Graphing Display of Numbers and Frequency Number display is oftern needed There are numerous ways to display the numbers Often just including a table is not enough

Spatial Information Technology Center Histograms Graphic records of the occurrence of data values in a statistical distribution They represent a statistical distibution better then if just displayed in a table Permit an easy inspectin of how the data values are arrayed along a number line Allow the reader to gather a rather detailed picture of overall data characteristics

Spatial Information Technology Center Frequency Polygons and Frequency Distributions Frequency polygon – created by joining the tops of the bars in a histogram May create the frequency curve If the data is reordered into an ascending format, then it is known as a Lorenze Curve

Spatial Information Technology Center Ogives and Probability Graphs Ogive – a cumulative percentage graph Given the name by Sir Francis Galton ( ) due to the resemblance to the curved rib of a Gothic vault By changing the horz. And vert. Axis an ogive can become a probability graph

Spatial Information Technology Center Box-Whisker Plots A box is drawn to that certain horizontal lines within and at the edges of box, aligned to the vertical axis of the graph, represent percentile values of the distribution Commonly percentile of 10, 25, 50, 75, 90 are represented

Spatial Information Technology Center Showing How Much of Something Linear Dot Graph Common Bar Graph One of the oldest forms of graphing Shows comparative amounts Clock graph (used by meteorologists for wind) Sector Graph Often called the pie graph Angles represent percentages; should not be done in 3D Trilinear Graph Soil – texture graph is common

Spatial Information Technology Center Showing Trends and Two- Variable Relation Graphs There are numerous ways to show trends and relationships within data Line Graphs Scatterplots Logarithmic Graphs

Spatial Information Technology Center Simple and Compound Line Graphs Line Graph To show the relationship between two variables Simple Line Graphs (time on the horizontal axis) Compound Line Graphs (multiple variables)

Spatial Information Technology Center The Scatterplot To see the mathematical relationship visually Vertical axis is dependent Horizontal axis is independent Each data point represents a paired value Often used to find statistical correlation May lead to finding a regression line Looks for a relationship between variables

Spatial Information Technology Center The Logarithmic Graph Must have a logarithmic scale on one axis Purpose of these is to show a rate of change of one variable vs. another