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GIS Tutorial 1
Lecture 2
Map design
Outline
Choropleth maps
Colors
Vector GIS display
GIS queries
Map layers and scale thresholds
Hyperlinks and map tips
GIS TUTORIAL 1 - Basic Workbook 2
CHOROPLETH MAPS
Lecture 2
Choropleth maps
Color-coded polygon maps
Use monochromatic scales or saturated
colors
Represent numeric values (e.g. population,
number of housing units, percentage of
vacancies)
GIS TUTORIAL 1 - Basic Workbook 4
Choropleth map example
Percentage of vacant housing units by
county
5 GIS TUTORIAL 1 - Basic Workbook
Classifying data
Process of placing data into groups (classes or
bins) that have a similar characteristic or value
Break points
Breaks the total attribute
range up into these intervals
Keep the number of intervals
as small as possible (5-7)
Use a mathematical progression
or formula instead of picking
arbitrary values
GIS TUTORIAL 1 - Basic Workbook 6
Break
points
Classifications
Natural breaks (Jenks)
Picks breaks that best group similar values
together naturally and maximizes the differences
between classes
Generally, there are relatively large jumps in
value between classes and classes are uneven
Based on a subjective decision and is the best
choice for combining similar values
Class ranges specific to the individual dataset,
thus it is difficult to compare a map with another
map
GIS TUTORIAL 1 - Basic Workbook 7
Classifications
Quantiles
Places the same number of data values in each
class
Will never have empty classes or classes with
too few or too many values
Attractive in that this method produces distinct
map patterns
Analysts use because they provide information
about the shape of the distribution.
Example: 0–25%, 25%–50%, 50%–75%,75%–
100%
GIS TUTORIAL 1 - Basic Workbook 8
Classifications
Equal intervals
Divides a set of attribute values into groups that
contain an equal range of values
Best communicates with continuous set of data
Easy to accomplish and read
Not good for clustered data
Produces map with many features in one or two classes
and some classes with no features
GIS TUTORIAL 1 - Basic Workbook 9
Classifications
Use mathematical formulas when possible.
Exponential scales
Popular method of increasing intervals
Use break values that are powers such as 2n or
3n
Generally start out with zero as an additional
class if that value appears in your data
Example: 0, 1–2, 3–4, 5–8, 9–16, and so forth
10 GIS TUTORIAL 1 - Basic Workbook
Classifications
Use mathematical formulas when possible
Increasing interval widths
Long-tailed distributions
Data distributions deviate from a bell-shaped
curve and most often are skewed to the right
with the right tail elongated
Example: Keep doubling the interval of each
category, 0–5, 5–15, 15–35, 35–75 have interval
widths of 5, 10, 20, and 40.
11 GIS TUTORIAL 1 - Basic Workbook
U.S. population by state, 2000
12 GIS TUTORIAL 1 - Basic Workbook
Original map (natural breaks)
Not good because too many values fall into low classes
13 GIS TUTORIAL 1 - Basic Workbook
Equal interval scale
Shows that an increasing width (geometric) scale is needed
14 GIS TUTORIAL 1 - Basic Workbook
Quantile scale
Custom geometric scale
Experiment with exponential scales with powers
of 2 or 3.
15 GIS TUTORIAL 1 - Basic Workbook
Divides one numeric attribute by another in order to
minimize differences in values based on the size of
areas or number of features in each area
Examples:
Dividing the number of vacant housing units by the
total number of housing units yields the percentage
of vacant units
Dividing the population by area of the feature yields
a population density
16 GIS TUTORIAL 1 - Basic Workbook
Normalizing data
Nonnormalized data
Number of vacant housing units by state, 2000
17 GIS TUTORIAL 1 - Basic Workbook
Normalized data
Percentage vacant housing units by state, 2000
18 GIS TUTORIAL 1 - Basic Workbook
California population by county, 2007
19 GIS TUTORIAL 1 - Basic Workbook
Nonnormalized data
20 GIS TUTORIAL 1 - Basic Workbook
California population density, 2007
Normalized data
COLORS
Lecture 2
21 GIS TUTORIAL 1 - Basic Workbook
22
Hue is the basic color
Value is the amount of white or black in the color
Saturation refers to a color scale that ranges
from a pure hue to gray or black
GIS TUTORIAL 1 - Basic Workbook
Color overview
23
Device that provides guidance in choosing colors
Use opposite colors to
differentiate graphic features
Three or four colors equally
spaced around the wheel are
good choices for differentiating
graphic features
Use adjacent colors for
harmony, such as blue, blue
green, and green or red, red
orange, and orange
GIS TUTORIAL 1 - Basic Workbook
Color wheel
Light colors associated with low values
Dark colors associated with high values
Human eye is drawn to dark colors
GIS TUTORIAL 1 - Basic Workbook 24
Light vs. dark colors
Contrast
The greater the difference in value between an
object and its background, the greater the
contrast
GIS TUTORIAL 1 - Basic Workbook 25
Monochromatic color scale
Series of colors of the same hue with color
value varied from low to high
Common for choropleth maps
The darker the color in a monochromatic
scale, the more important the graphic feature
Use more light shades of a hue than dark
shades in monochromatic scales
The human eye can better differentiate among
light shades than dark shades
26 GIS TUTORIAL 1 - Basic Workbook
Monochromatic map
Values too similar
27 GIS TUTORIAL 1 - Basic Workbook
Monochromatic map
A better map, more contrast
28 GIS TUTORIAL 1 - Basic Workbook
29
An exception to the typical monochromatic
scale used in most choropleth maps
Two monochromatic scales joined together
with a low color value in the center, with color
value increasing toward both ends
Uses a natural middle point of a scale, such as
0 for some quantities (profits and losses,
increases and decreases)
GIS TUTORIAL 1 - Basic Workbook
Dichromatic color scale
30 GIS TUTORIAL 1 - Basic Workbook
Symmetric break points centered on 0 make it easy to
interpret the map
Dichromatic map
Color tips
Colors have meaning
Political and cultural
Cool colors
Calming
Appear smaller
Recede
Warm colors
Exciting
Overpower cool colors
31 GIS TUTORIAL 1 - Basic Workbook
32
Do not use all of the colors of the color
spectrum, as seen from a prism or in a
rainbow, for color coding
If you have relatively few points in a point
layer, or if a user will normally be zoomed in
to view parts of your map, use size instead
of color value to symbolize a numeric
attribute
GIS TUTORIAL 1 - Basic Workbook
Color tips
33
If you have many polygons to symbolize, it is better to
use polygon centroid points with color rather than
polygon choropleth maps.
GIS TUTORIAL 1 - Basic Workbook
Color tips
Changing colors in ArcMap
Choose color, more colors…
34 GIS TUTORIAL 1 - Basic Workbook
Website
http://colorbrewer2.org/
Books
Brewer, Cynthia A. 2008. Designed Maps: A
Sourcebook for GIS Users. Redlands: ESRI
Press
Brewer, Cynthia A. 2005. Designing Better Maps:
A Guide for GIS Users. Redlands: ESRI Press
GIS TUTORIAL 1 - Basic Workbook 35
Learn more about GIS colors
VECTOR GIS DISPLAY
Lecture 2
36 GIS TUTORIAL 1 - Basic Workbook
Points, lines, polygons
Point
x,y coordinates
Line
starting and ending point and may have
additional shape vertices (points)
Polygon
three or more lines joined to form a closed area
37 GIS TUTORIAL 1 - Basic Workbook
Feature attribute tables
Store characteristics for vector features
Layers can be displayed using attributes
38 GIS TUTORIAL 1 - Basic Workbook
Displaying points
Single symbols
All CAD calls
39 GIS TUTORIAL 1 - Basic Workbook
Displaying points
Same features, different points
Based on attributes
GIS TUTORIAL 1 - Basic Workbook 40
Displaying points
Industry specific (e.g. crime analysis)
Good for large scale (zoomed in) maps
GIS TUTORIAL 1 - Basic Workbook 41
Displaying points
Industry specific (e.g. schools)
Not good for multiple features at smaller scales
Simple points better for analysis
GIS TUTORIAL 1 - Basic Workbook 42
Displaying points
Quantities
Use exaggerated sizes
GIS TUTORIAL 1 - Basic Workbook 43
Displaying lines
For analytical maps, most lines are ground
features and should be light shades (e.g. gray
or light brown)
GIS TUTORIAL 1 - Basic Workbook 44
Displaying lines
Consider using dashed lines to signify less
important line features and solid lines for the
important ones
GIS TUTORIAL 1 - Basic Workbook 45
Displaying polygons
Consider using no outline or dark gray for
boundaries of most polygons
Dark gray makes the polygons prominent
enough, but not so much that they compete for
attention with more important graphic features
GIS TUTORIAL 1 - Basic Workbook 46
Displaying polygons
Consider using texture for black and white
copies
GIS TUTORIAL 1 - Basic Workbook 47
Assign bright colors (red, orange, yellow, green,
blue) to important graphic elements
Features are known as figure
All features in figure
GIS TUTORIAL 1 - Basic Workbook 48
Graphic hierarchy
Assign drab colors to the graphic elements that
provide orientation or context, especially shades
of gray
Features known as ground
49
Circles in figure, squares and lines in
ground
GIS TUTORIAL 1 - Basic Workbook 49
Graphic hierarchy
Place a strong boundary, such as a heavy black
line, around polygons that are important to
increase figure
Use a coarse, heavy cross-hatch or pattern to
make some polygons important, placing them in
figure
GIS TUTORIAL 1 - Basic Workbook
Graphic hierarchy
50
GIS TUTORIAL 1 - Basic Workbook 51
Graphic hierarchy example
GIS QUERIES
Lecture 2
52 GIS TUTORIAL 1 - Basic Workbook
53
Powerful relationship between data table
and vector-based graphics—unique to GIS
Records from a feature attribute table are
selected by using query criteria
Query will automatically highlight the
corresponding graphic features
GIS TUTORIAL 1 - Basic Workbook
GIS queries
54
Simple query criterion
<data attribute>< logical operator><value>
NatureCode ='DRUGS'
DATE >= '20040701'
% wild card
% symbol stands for zero, one, or more characters
of any kind
NAME like ' BUR%'
Selects any crime with names starting with the
letters BUR, including burglaries (BUR), business
burglaries(BURBUS), and residential burglaries
(BURRES) GIS TUTORIAL 1 - Basic Workbook
Simple attribute queries
GIS TUTORIAL 1 - Basic Workbook 55
Simple attribute queries
56
Compound query criteria
Combine two or more simple queries with the
logical connectives AND or OR
"NATURE_COD" = 'DRUGS' AND "DATE" >
20040801
Selects records that satisfy both criteria
simultaneously
Result are drug crimes that were committed after
August 1, 2004
GIS TUTORIAL 1 - Basic Workbook
Compound attribute queries
GIS TUTORIAL 1 - Basic Workbook 57
Compound attribute queries
LAYER GROUPS, SCALE THRESHOLDS
Lecture 2
Layer groups
Organizes layers
Groups and names logically
GIS TUTORIAL 1 - Basic Workbook 59
Minimum scale threshold
When zoomed out beyond this scale,
features will not be visible
Tracts not visible when zoomed to the USA
60 GIS TUTORIAL 1 - Basic Workbook
Minimum scale threshold
Tracts displayed when zoomed in
61 GIS TUTORIAL 1 - Basic Workbook
Maximum scale threshold
When zoomed in, features will not be visible
State population will disappear when zoomed in
to a state
62 GIS TUTORIAL 1 - Basic Workbook
HYPERLINKS AND MAP TIPS
Lecture 2
Links images, documents, Web pages, etc.
to features on a map
GIS TUTORIAL 1 - Basic Workbook 64
Hyperlinks
Map tips
Provide an additional way to find information
about map features
Pop up as you hover the mouse pointer over
a feature
65 GIS TUTORIAL 1 - Basic Workbook
Summary
Choropleth maps
Colors
Vector GIS display
GIS queries
Map layers and scale thresholds
Hyperlinks and Map tips
GIS TUTORIAL 1 - Basic Workbook 66