1. Chapter 2
Mapping GIS Data

2. Outline GIS Concepts Mapping GIS data Displaying rasters
Classifying numeric data

3. Mapping GIS data Map type Data type Nominal data Categorical data
Ordinal data
Interval and Ratio data
Single symbol map
Unique values maps
Quantities maps
Graduated color
Graduated symbol
Dot density

4. Nominal Data Names or uniquely identifies objects
State names
Owner of parcel
Tax ID number
Parcel ID Number
Each feature likely to have its own value
Usually portrayed on a map as labels

5. Single symbol maps Display all features with the same symbol
Combine with labels to portray nominal data

6. Categorical data
Places features into defined number of distinct categories
Category names may be text or numeric
Portrayed by different symbol for each category

7. Unique values maps
Different symbol for each category or value

8. Ordinal data Type of categorical data
Ranks categories along an arbitrary scale
Low, Medium, High slope
Village, Town, City
Grades: A, B, C, D, F
Rank of Best City to Live In: 1, 2, 3…

9. Interval and Ratio data
Interval data places values along a regular numeric scale
Supports addition and subtraction
Temperature, pH, and elevation
Ratio data places values along a regular scale with a meaningful zero point
Supports addition, subtraction, multiplication, and division
Population, rainfall, and median rent

10. Mapping numeric data
Interval and ratio data must be divided into classes before mapping
Mapped using variations in symbol size, thickness, or hue

11. Classed maps Graduated color map (choropleth map)
Simply color variation
Graduated symbol map
Symbol size variation
Normalized map

12. Unclassed maps
Proportional symbol map
Dot density map

13. Displaying rasters Discrete data Continuous data
Represents discrete objects such as lines or polygons
Takes on relatively few values
Adjacent cells often have same values
Values may change abruptly at boundaries
Continuous data
Thousands or millions of potential values
Few adjacent cells have same values
Values may change rapidly from cell to cell

14. Raster types Thematic rasters Image rasters
Contain quantities that represent map data such as land use or rainfall
May be continuous or discrete
Image rasters
Contain satellite or air photo data
Generally represent brightness
Usually continous

15. Classifying numeric data
Applies to both vector and raster maps
Different classification methods available
Choice impacts map appearance and validity
Best method depends on data distribution and objective of map
Same data, different classifications

16. Classifying types 1. Jenks Natural Breaks 2. Equal Interval
Exploits natural gaps in the data
Good for unevenly distributed or skewed data
Default method, works well for most data sets
2. Equal Interval
Specify number of classes
Divides into equally spaced classes
Works best for uniformly distributed data
3. Defined interval
User chooses the class size
Data determines number of classes

17. Classifying types cont..
4. Quantile
Same number of features in each class
May get very unevenly spaced class ranges
Results depend on data distribution
5. Geometrical Interval
Multiplies each succeeding class boundary by a constant
Works well for normal and skewed distributions
6. Standard Deviation
Shows deviation from mean
User chooses units e.g. 0.5 standard deviations
Assumes data are normally distributed

18. References Price, M. (2013). Mastering ArcGIS (6th ed.). McGraw-Hill
Price, M. (2013). Mastering ArcGIS (6th ed.). McGraw-Hill. Mastering ArcGIS, 6/e Instructor Edition Chapter 2: PowerPoint Notes and Figures