Intro to GIS Summer 2012 Data Visualization

Intro to GIS Summer 2012 Data Visualization

UNDERSTANDING YOUR MAP DATA

Qualitative vs. Quantitative Data Qualitative Data classified by category e.g. Soil types, Animal Species Quantitative Data grouped by numerical value e.g. Population (# of people), Forest cover (%) Why is understanding this so important? Data type will influence your choice of map symbolization and visualization

DATA ATTRIBUTE TYPES

What Types of Attributes can be shown on a map? Nominal Ordinal Interval Ratio (Cyclic)

Establish the group, class, member, or category with which an object is associated; or Identify one instance from another Qualitative, not quantitative data. Nominal Attributes

Ordinal (Ranked) Attributes Show place in a ranking, e.g. 1 st, 2 nd, 3 rd, etc. Better vs. worse, higher vs. lower, etc. Does not establish magnitude; cannot demonstrate how much better or worse, etc. Quantitative data

Interval Attributes Numerical values derived from a linear calibrated scale There is no true zero point on the scale Appropriate for showing relative comparisons between measurements; mathematical operations on this kind of data will not have meaningful results e.g. Time of day, most temperature scales Quantitative data

Ratio Attributes Numerical values derived from a linear calibrated scale Relative to a fixed zero point Mathematical operations can be used on these values with predictable and meaningful results Examples: Age, Distance, Cost, Elevation Quantitative data

Which Attributes are in my Data? The software does not decide between nominal ordinal interval ratio data. Who does? That would be you The Cartographer

Displaying data attributes in ArcMap ArcMap Method Point Line Area Raster Feature (shows location) Nominal Ordinal Interval Cyclic Ratio Nominal Ordinal Interval Cyclic Ratio Nominal Ordinal Interval Cyclic Ratio Categories - Unique values Nominal Nominal Nominal Nominal Quantities -Graduated color -Graduated symbols -Proportional symbols Ordinal Interval Cyclic Ratio Ordinal Interval Cyclic Ratio Ordinal Interval Cyclic Ratio Ordinal Interval Cyclic Ratio Charts Ratio Ratio Ratio Multiple Ratio Ratio Ratio David Theobald

SHOWING QUALITATIVE DATA ON MAPS

Features (Showing Location) Each geographic feature is represented by a single color

Categories (Unique Values) Each geographic feature is represented by a different color

Categories (Unique Values Grouped) Geographic features are grouped and each group is represented by a color

SHOWING QUANTITATIVE DATA ON MAPS

Quantitative Map Types Choropleth (Classification) Isoline Cartogram Density New types of Visualization

CHOROPLETH MAPS & DATA CLASSIFICATION

Choropleth Maps Widely-used method for showing quantitative data Based on numeric attributes of non-overlapping areas Areas are shaded based on the value of the attribute Spatially-sensitive values should be normalized Convert raw count data to ratio (density); this is done by dividing raw data by another attribute (e.g. area) e.g. Raw count data: Total Population per County e.g. Density data: Population/mi 2 per County

How do these % values get grouped into classes?

Classification Methods Different ways to show how data is grouped into classes Classification goals: Make the map easy to read and understand Communicate info that is not self-evident about an area Cartographer must decide which method to use

Natural Breaks (Jenks) Method Classes are based on natural groupings of data Statistical method that minimizes the total variance within each group (i.e. similar things are put into the same group) Cartographer sets number of classes; ArcMap finds natural groupings

Quantile Method Each class contains (approx) the same # of features Best suited for data that is uniformly distributed; data that does not have a disproportionate number of features with similar values Cartographer sets number of classes; ArcMap assigns data to each class

Interval Methods Equal Intervals: Features are divided equally into a set number of intervals. Cartographer sets number of intervals (e.g. 3); ArcMap calculates interval range (e.g. 0-5, 6-10, 11-15 etc.) and assigns data to each interval. Defined Intervals: Features are divided based on a set interval range. Cartographer sets intervals (e.g. 0-7, 7-9, 9-15); ArcMap assigns data to each interval.

Standard Deviation Method Shows distance from the data mean (average) Places class breaks at intervals (1/4, 1/5, or 1) away from mean, based on the type of standard deviation Cartographer sets type; ArcMap assigns data to intervals

Normal Distribution Curve

Which method(s) are appropriate for data values that naturally clump into different groups?

Which method(s) are appropriate for data that has uniformly distributed values?

Which method(s) are appropriate for data values that follows a normal distribution?

Classification Methods Natural groupings of features into classes Features classified by distance from mean Class values are equally spaced Same # of features in each class

Normalizing Data When geographic features vary in size, then data should be displayed as densities; i.e. Spatiallysensitive values should be normalized Raw count data converted to a ratio (density) Divide raw data by another attribute (e.g. area) Let s look at a visual example

If Raw count data is Total Population per State, then

The corresponding density is Population per mi 2 (by State)

ISOLINE MAPS

Isoline Maps Lines joining points of equal value (usually generalized) Used for continuous surfaces; phenomena must vary smoothly across the map Common example is contour lines but isolines can show other data besides elevation! Two types: Isometric (measured values) Isopleth (areal averages)

Example - Isometric map

Example - Isopleth map

CARTOGRAMS

Cartograms Distort area, shape or distance of map symbols for a specific purpose Reveal or enhance patterns that might not be visually apparent on a normal map Sometimes used to promote legibility

WorldMapper World Population Atlas www.worldpopulationatlas.org

DENSITY MAPS

Density Maps Uniform symbols repeated across map Exact quantities not shown Instead, goal is to give an overall impression of data distribution across an area (i.e. density) Distribution of symbols represents distribution of data

NEW TYPES OF VISUALIZATION

3D Visualization

3D Visualization

Temporal Visualization GAPMINDER WORLD Hans Rosling Statistics shown using Graphs & Maps http://www.gapminder.org/world

Interactive/Crowd-Sourced Visualizations TED Talk: Aaron Koblin Artfully visualizing our humanity www.ted.com/talks/aaron_koblin.html www.aaronkoblin.com/work/flightpatterns

ADVANCED MAP DESIGN

Elements of Good Map Design If a map is Graphically balanced Easy to read Limits redundant or unnecessary information Then it will Communicate a strong visual message to audience Convey the intended information (i.e. function properly) Satisfy purpose of designer (or the client!)

Map Layout Map Elements Components of map layout Main Map Visual representation of data What is the main map called in ArcMap?

Map Layout Visual Hierarchy how different elements are positioned on the map, e.g. Color contrast Line weights Amount of detail

Possible Improvements Class Discussion: How else would you improve the layout for this map?

Refining Map Layout

Poor Attention to Detail Good Attention to Detail

Choosing Appropriate Map Projections

Decorative Design Elements

Same Map Emphasizing important map content, not decorative elements

MAP DESIGN RESOURCES

Resources for Map Design General Resources Designing Better Maps, Cynthia Brewer How to Lie With Maps, Mark Monmonier Making Maps: A Visual Guide to Map Design for GIS, John Krygier How Maps Work: Representation, Visualization, and Design, Alan M. MacEachren The Power of Maps, Denis Wood Especially for Color Blindness vcgiblog.wordpress.com/2010/11/02/designing-maps-for-the-color-blind/ www.vischeck.com/vischeck/ colororacle.org/ mappingcenter.esri.com/index.cfm?fa=arcgisresources.gateway#arcgisresourcescd freegeographytools.com/2008/evaluating-map-graphics-for-color-blind-viewers